performance boost for String#blank? in Ruby 2.4

Some casual benchmarks showed a 2x factor.

All credit goes to @nurse.

activesupport/lib/active_support/core_ext/object/blank.rb

@@ -115,7 +115,7 @@ def blank?
     # The regexp that matches blank strings is expensive. For the case of empty
     # strings we can speed up this method (~3.5x) with an empty? call. The
     # penalty for the rest of strings is marginal.
-    empty? || BLANK_RE === self
+    empty? || BLANK_RE.match?(self)
   end
 end