fix style

Author: braised-babbage

source/openpulse/openpulse/parser.py

@@ -87,11 +87,11 @@ def parse_openpulse(
     try:
         tree = parser.calibrationBlock()
     except (RecognitionException, ParseCancellationException) as exc:
-        msg = ''
+        msg = ""
         # With BailErrorStrategy, we should be able to recover and report
         # information about the offending token.
         if isinstance(exc, ParseCancellationException) and exc.args:
-            tok = getattr(exc.args[0], 'offendingToken', None)
+            tok = getattr(exc.args[0], "offendingToken", None)
             if tok is not None:
                 msg = f"Unexpected token '{tok.text}' at line {tok.line}, column {tok.start}."
         raise OpenPulseParsingError(msg) from exc