[PRISM] Enable passing regexp test

Author: kddnewton

test/.excludes-prism/TestRegexp.rb

@@ -1,6 +1,5 @@
 exclude(:test_unicode_age_14_0, "unknown")
 exclude(:test_invalid_fragment, "unknown")
-exclude(:test_assign_named_capture_to_reserved_word, "unknown")
 exclude(:test_unicode_age_15_0, "unknown")
 exclude(:test_unescape, "unknown")
 exclude(:test_invalid_escape_error, "unknown")