Add .fcgi as an extension for script languages

This PR adds `.fcgi` as an extension for script languages.
Currently all `.fcgi` files are recognized as Perl.
Many incorrectly identified files can be found on GitHub with this extension:
- [Bash files](https://github.com/search?utf8=%E2%9C%93&q=extension%3Afcgi+bash&type=Code&ref=searchresults)
- [Lua files ](https://github.com/search?utf8=%E2%9C%93&q=extension%3Afcgi+lua&type=Code&ref=searchresults)
- [PHP files](https://github.com/search?utf8=%E2%9C%93&q=extension%3Afcgi+php&type=Code&ref=searchresults)
- [Python files](https://github.com/search?utf8=%E2%9C%93&q=extension%3Afcgi+python&type=Code&ref=searchresults)
- [Ruby files](https://github.com/search?utf8=%E2%9C%93&q=extension%3Afcgi+ruby&type=Code&ref=searchresults)

These files almost always contain a shebang and should be correctly identified once this PR is merged.