Use Regexp#=~ for ruby 2.3

`Regexp#match?` was introduced at ruby 2.4.

Author: nobu

lib/core_assertions.rb

@@ -18,11 +18,11 @@ def filter bt
 
       unless $DEBUG then
         bt.each do |line|
-          break if pattern.match?(line)
+          break if pattern =~ line
           new_bt << line
         end
 
-        new_bt = bt.reject { |line| pattern.match?(line) } if new_bt.empty?
+        new_bt = bt.reject { |line| pattern =~ line } if new_bt.empty?
         new_bt = bt.dup if new_bt.empty?
       else
         new_bt = bt.dup