Added new file to ruby_EXTRA_DIST.

Makefile.am

@@ -705,6 +705,7 @@ ruby_EXTRA_DIST=                                                             \
   ruby/tests/repeated_field_test.rb                                          \
   ruby/tests/stress.rb                                                       \
   ruby/tests/generated_code.proto                                            \
+  ruby/tests/test_import.proto                                               \
   ruby/tests/generated_code_test.rb                                          \
   ruby/travis-test.sh