message: Added test that error line numbers are correct for invalid code
  <rdar://problem/46408318>
diff: @@ -46,7 +46,8 @@ class TestInvalidInput(repl.PlaygroundREPLTest):
  is_error = self.is_compile_or_runtime_error(result)
  self.assertTrue(is_error)
  error = self.get_stream_data(result)
  - self.assertTrue("left side of mutating operator" in error)
  + self.assertIn("left side of mutating operator", error, "Error messages do not match")
  + self.assertIn(":15:3: error: left side of mutating operator", error, "Error line number does not match")
  # Execute revised block
  result, output = self.execute_code("Input3.swift")
  