Failed to search with `422 Unprocessable Entity`

[kyoshidajp]

Failed to search when a keyword has :.

% ghkw -d language:ruby
2018/02/07 21:12:08 [DEBUG] Run as DEBUG mode
2018/02/07 21:12:08 [DEBUG] keyword: [language:ruby]
422 Unprocessable Entity
&{%!s(*http.bodyEOFSignal=&{0xc4203d4940 {0 0} true 0xc420046060 <nil> 0x11fbc70}) %!s(func()=<nil>)}
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x1291e67]

goroutine 22 [running]:
main.(*Searcher).searchRequest(0xc420244420, 0x7ffeefbff728, 0xd, 0xc42007c1e0)
        /Users/katsuhiko.yoshida/go/src/github.com/kyoshidajp/ghkw/cli.go:134 +0x2a7
created by main.(*Searcher).search
        /Users/katsuhiko.yoshida/go/src/github.com/kyoshidajp/ghkw/cli.go:144 +0xbf

Run successfully without :.

% ghkw -d languageruby
2018/02/07 21:13:07 [DEBUG] Run as DEBUG mode
2018/02/07 21:13:07 [DEBUG] keyword: [languageruby]
2018/02/07 21:13:09 [DEBUG] Keyword: languageruby (32)
| RANK |   KEYWORD    | TOTAL |
|------|--------------|-------|
|    1 | languageruby |    32 |

According to GitHub Search Document, Search query can't include . , : ; / \ ` ' " = * ! ? # $ & + ^ | ~ < > ( ) { } [ ].