Convert to boolean in C code

casecmp?(str) is 1.5x faster than casecmp(str).zero?
It's 1 less method call in Ruby, and the C code can convert
to boolean, rather than returning a number and determining
if it's zero.

app/helpers/jsonld_helper.rb

@@ -53,7 +53,7 @@ module JsonLdHelper
     needle   = Addressable::URI.parse(url).host
     haystack = Addressable::URI.parse(@account.uri).host
 
-    !haystack.casecmp(needle).zero?
+    !haystack.casecmp?(needle)
   end
 
   def canonicalize(json)