sqlite3 link error

the command in the Makefile fails
```bash
$ gcc -lsqlite3 main.c -o bitcloud
/tmp/ccc6Ff3X.o: In function `main':
main.c:(.text+0x1c): undefined reference to `sqlite3_open'
main.c:(.text+0x31): undefined reference to `sqlite3_errmsg'
main.c:(.text+0x59): undefined reference to `sqlite3_close'
collect2: error: ld returned 1 exit status
```
It should be
```bash
gcc main.c -o bitcloud -lsqlite3
```