Fix text decoration parsing (#473)

[Foorcee]

Fix #473

Relates to: https://github.com/google/gson/blob/master/gson/src/main/java/com/google/gson/JsonPrimitive.java#L100

[kashike]

Please add some test coverage for this.

[Proximyst]

This won't work with e.g. 1 as I see the intention here. Boolean#parseBoolean:

    public static boolean parseBoolean(String s) {
        return "true".equalsIgnoreCase(s);
    }

[Foorcee]

Compared to JsonPrimitive#getAsBoolean():

  @Override
  public boolean getAsBoolean() {
    if (isBoolean()) {
      return ((Boolean) value).booleanValue();
    }
	// Check to see if the value as a String is "true" in any case.
    return Boolean.parseBoolean(getAsString());
  }

The method, is used by the client in Style.Serializer.