Fix missing test dependency

I got following error when testing.

```
% prove -bv t/002_action.t 
t/002_action.t .. core - engine - unable to load template engine 'HtmlTemplate' (perhaps you need to install Dancer::Template::HtmlTemplate?): Can't locate Dancer/Template/HtmlTemplate.pm in @INC (you may need to install the Dancer::Template::HtmlTemplate module) (@INC contains: /home/syohei/.cpanm/work/1411784973.10012/Dancer-Plugin-Controller-0.152/perl-dancer-plugin-controller/t/lib /home/syohei/.cpanm/work/1411784973.10012/Dancer-Plugin-Controller-0.152/perl-dancer-plugin-controller/t/../lib /home/syohei/.cpanm/work/1411784973.10012/Dancer-Plugin-Controller-0.152/perl-dancer-plugin-controller/blib/lib /home/syohei/.cpanm/work/1411784973.10012/Dancer-Plugin-Controller-0.152/perl-dancer-plugin-controller/blib/arch /home/syohei/.opam/4.01.0/lib/perl5 /home/syohei/.plenv/versions/5.20.1/lib/perl5/site_perl/5.20.1/x86_64-linux-thread-multi /home/syohei/.plenv/versions/5.20.1/lib/perl5/site_perl/5.20.1 /home/syohei/.plenv/versions/5.20.1/lib/perl5/5.20.1/x86_64-linux-thread-multi /home/syohei/.plenv/versions/5.20.1/lib/perl5/5.20.1 .) at /home/syohei/.plenv/versions/5.20.1/lib/perl5/site_perl/5.20.1/Module/Runtime.pm line 317.
 at /home/syohei/.plenv/versions/5.20.1/lib/perl5/site_perl/5.20.1/Dancer/Template.pm line 21.
BEGIN failed--compilation aborted at t/002_action.t line 14.
# Looks like your test exited with 2 before it could output anything.
Dubious, test returned 2 (wstat 512, 0x200)
No subtests run 

Test Summary Report
-------------------
t/002_action.t (Wstat: 512 Tests: 0 Failed: 0)
  Non-zero exit status: 2
  Parse errors: No plan found in TAP output
Files=1, Tests=0,  0 wallclock secs ( 0.03 usr  0.01 sys +  0.30 cusr  0.02 csys =  0.36 CPU)
Result: FAIL
```