Add stub for breaking spec filter

Author: adambeynon

opal/opal/rspec/fixes.rb

@@ -7,6 +7,13 @@ def flat_map(array)
   module_function :flat_map
 end
 
+# This breaks on 2.0.0, so it is here ready for when opal bumps to 2.0.0
+class RSpec::CallerFilter
+  def self.first_non_rspec_line
+    ""
+  end
+end
+
 # String#<< is not supported by Opal
 module RSpec::Expectations
   def self.fail_with(message, expected = nil, actual = nil)