denote utf-8 encoding

This fixes an issue there the ruby interpreter runs into a syntax error because it can't interpret the unicode symbol for "greater than or equal" for the cli tool:
```
/Users/mrtazz/bin/vimr:17: invalid multibyte char (US-ASCII)
/Users/mrtazz/bin/vimr:14: syntax error, unexpected $end, expecting tSTRING_CONTENT or tSTRING_DBEG or tSTRING_DVAR or tSTRING_END
```