add Crystal type: "Projectfile", "*.cr"

https://en.wikipedia.org/wiki/Crystal_(programming_language)
https://github.com/rhysd/vim-crystal/blob/master/ftdetect/crystal.vim

ignore/src/types.rs

@@ -112,6 +112,7 @@ const DEFAULT_TYPES: &'static [(&'static str, &'static [&'static str])] = &[
         "*.C", "*.cc", "*.cpp", "*.cxx",
         "*.h", "*.H", "*.hh", "*.hpp",
     ]),
+    ("crystal", &["Projectfile", "*.cr"]),
     ("cs", &["*.cs"]),
     ("csharp", &["*.cs"]),
     ("css", &["*.css"]),