remove ruby version specification
remove ruby version specification

hopefully removes this error on Travis;
```
ERROR:  Error installing html-proofer:
	activesupport requires Ruby version >= 2.2.2.
The command "gem install html-proofer" failed and exited with 1 during 
```
redcap-tools/redcap-tools.github.io,redcap-tools/redcap-tools.github.io