fix: add missing slash when defining RainTPL's temp dir

Hi!

I just (8th of October) switched from sebsauvage's upstream repo to this one, and saw some RainTPL temp files appear at the root of the installation:

```bash
virtualtam( /path/to/shaarli ) $ ls -lah
total 388K
drwxrwxr-x 2 virtualtam www-data   4.0K Oct  9 01:47 cache
-rw-r--r-- 1 virtualtam virtualtam 3.5K Oct  8 21:58 COPYING
drwxrwxr-x 2 virtualtam www-data   4.0K Oct  8 21:58 data
drwxrwxr-x 2 virtualtam www-data   4.0K Oct  8 21:58 images
drwxrwxr-x 2 virtualtam www-data   4.0K Oct  8 21:58 inc
-rw-r--r-- 1 virtualtam virtualtam 118K Oct 19 00:55 index.php
drwxrwxr-x 2 virtualtam www-data   164K Oct 19 00:14 pagecache
-rw-r--r-- 1 virtualtam virtualtam 3.5K Oct  8 21:58 README.md
drwxrwxr-x 2 virtualtam www-data   4.0K Oct  8 21:58 tmp
-rw-r--r-- 1 www-data   www-data    983 Oct  8 21:58 tmpaddlink.9097c979923185181c80a7f04e7d4686.rtpl.php
-rw-r--r-- 1 www-data   www-data   2.8K Oct  8 21:26 tmpconfigure.9097c979923185181c80a7f04e7d4686.rtpl.php
-rw-r--r-- 1 www-data   www-data   5.7K Oct  9 03:02 tmpdaily.9097c979923185181c80a7f04e7d4686.rtpl.php
-rw-r--r-- 1 www-data   www-data   3.2K Oct  8 21:58 tmpeditlink.9097c979923185181c80a7f04e7d4686.rtpl.php
-rw-r--r-- 1 www-data   www-data   1.1K Oct 18 21:10 tmpexport.9097c979923185181c80a7f04e7d4686.rtpl.php
-rw-r--r-- 1 www-data   www-data    875 Oct  8 21:58 tmpincludes.d0a73bb58c8af06f173bc0c08466128e.rtpl.php
-rw-r--r-- 1 www-data   www-data   7.7K Oct  8 21:58 tmplinklist.9097c979923185181c80a7f04e7d4686.rtpl.php
-rw-r--r-- 1 www-data   www-data   1.2K Oct  8 21:58 tmplinklist.paging.d0a73bb58c8af06f173bc0c08466128e.rtpl.php
-rw-r--r-- 1 www-data   www-data   1.7K Oct 12 12:41 tmploginform.9097c979923185181c80a7f04e7d4686.rtpl.php
-rw-r--r-- 1 www-data   www-data    901 Oct  8 21:58 tmppage.footer.d0a73bb58c8af06f173bc0c08466128e.rtpl.php
-rw-r--r-- 1 www-data   www-data   1.4K Oct  8 21:58 tmppage.header.d0a73bb58c8af06f173bc0c08466128e.rtpl.php
-rw-r--r-- 1 www-data   www-data   1.6K Oct  8 22:54 tmppicwall.9097c979923185181c80a7f04e7d4686.rtpl.php
-rw-r--r-- 1 www-data   www-data   1.3K Oct 10 04:32 tmptagcloud.9097c979923185181c80a7f04e7d4686.rtpl.php
-rw-r--r-- 1 www-data   www-data   2.3K Oct 18 21:10 tmptools.9097c979923185181c80a7f04e7d4686.rtpl.php
drwxrwxr-x 2 virtualtam www-data   4.0K Oct  8 21:58 tpl
```

Adding a slash to the tmp dir declaration fixes the issues, new temp files appear in `./tmp/`:
```bash
virtualtam( /path/to/shaarli ) $ ls -lah tmp
total 72K
-rwxrwxr-x 1 virtualtam www-data  983 May  8 14:48 addlink.9097c979923185181c80a7f04e7d4686.rtpl.php
-rwxrwxr-x 1 virtualtam www-data 1.5K May  8 14:48 changetag.9097c979923185181c80a7f04e7d4686.rtpl.php
-rw-r--r-- 1 www-data   www-data 2.6K Jul  5 22:15 configure.9097c979923185181c80a7f04e7d4686.rtpl.php
-rwxrwxr-x 1 virtualtam www-data 5.7K Oct 19 01:04 daily.9097c979923185181c80a7f04e7d4686.rtpl.php
-rwxrwxr-x 1 virtualtam www-data  772 May  8 14:48 dailyrss.9097c979923185181c80a7f04e7d4686.rtpl.php
-rwxrwxr-x 1 virtualtam www-data 2.8K May  8 14:48 editlink.9097c979923185181c80a7f04e7d4686.rtpl.php
-rwxrwxr-x 1 virtualtam www-data  875 Oct 19 00:55 includes.d0a73bb58c8af06f173bc0c08466128e.rtpl.php
-rwxrwxr-x 1 virtualtam www-data 1.3K May  8 14:48 install.9097c979923185181c80a7f04e7d4686.rtpl.php
-rwxrwxr-x 1 virtualtam www-data 7.7K Oct 19 00:55 linklist.9097c979923185181c80a7f04e7d4686.rtpl.php
-rwxrwxr-x 1 virtualtam www-data 1.2K Oct 19 00:55 linklist.paging.d0a73bb58c8af06f173bc0c08466128e.rtpl.php
-rwxrwxr-x 1 virtualtam www-data 1.7K May  8 14:48 loginform.9097c979923185181c80a7f04e7d4686.rtpl.php
-rwxrwxr-x 1 virtualtam www-data  901 Oct 19 00:55 page.footer.d0a73bb58c8af06f173bc0c08466128e.rtpl.php
-rwxrwxr-x 1 virtualtam www-data 1.4K Oct 19 00:55 page.header.d0a73bb58c8af06f173bc0c08466128e.rtpl.php
-rwxrwxr-x 1 virtualtam www-data 1.5K May  8 14:48 picwall.9097c979923185181c80a7f04e7d4686.rtpl.php
-rwxrwxr-x 1 virtualtam www-data 1.3K Oct  8 21:24 tagcloud.9097c979923185181c80a7f04e7d4686.rtpl.php
-rwxrwxr-x 1 virtualtam www-data 2.3K May  8 14:48 tools.9097c979923185181c80a7f04e7d4686.rtpl.php
```