Use Regexp#match? to avoid extra allocations

`#=~` builds `MatchData`, requiring extra allocations as compared to
`#match?`, which returns a boolean w/o having to build the `MatchData`.

lib/uri/common.rb

@@ -397,7 +397,7 @@ def self.encode_www_form_component(str, enc=nil)
   #
   # See URI.encode_www_form_component, URI.decode_www_form.
   def self.decode_www_form_component(str, enc=Encoding::UTF_8)
-    raise ArgumentError, "invalid %-encoding (#{str})" if /%(?!\h\h)/ =~ str
+    raise ArgumentError, "invalid %-encoding (#{str})" if /%(?!\h\h)/.match?(str)
     str.b.gsub(/\+|%\h\h/, TBLDECWWWCOMP_).force_encoding(enc)
   end