API compatibility issue

[philippb]

• [x] I have verified the issue exists on the latest version
• [x] I am able to reproduce it

Version used: 1.13.0 Stack trace:

* What went wrong:
Execution failed for task ':taptargetview:lint'.
> Lint found errors in the project; aborting build.

  Fix the issues identified by lint, or add the following to your build script to proceed with errors:
  ...
  android {
      lintOptions {
          abortOnError false
      }
  }
  ...

  Errors found:

  /Users/philipp/coding/TapTargetView/taptargetview/src/main/java/com/getkeepsafe/taptargetview/ToolbarTapTarget.java:61: Error: Class requires API level 21 (current min is 14): android.widget.Toolbar [NewApi]
      } else if (instance instanceof android.widget.Toolbar) {
                                     ~~~~~~~~~~~~~~~~~~~~~~
  /Users/philipp/coding/TapTargetView/taptargetview/src/main/java/com/getkeepsafe/taptargetview/ToolbarTapTarget.java:62: Error: Class requires API level 21 (current min is 14): android.widget.Toolbar [NewApi]
        return new StandardToolbarProxy((android.widget.Toolbar) instance);
                                         ~~~~~~~~~~~~~~~~~~~~~~

Android version: Lint error