Manifest merger failed : uses-sdk:minSdkVersion 19 cannot be smaller than version 21 declared in library [:avenginekit] D:\Android\WorkSpace\android-chat-api-19\avenginekit\build\.transforms\58fc046de2f557f4c7c4987efff0d756\jetified-avenginekit\AndroidManifest.xml as the library might be using APIs not available in 19
Suggestion: use a compatible library with a minSdk of at most 19,
    or increase this project's minSdk version to at least 21,
    or use tools:overrideLibrary="cn.wildfirechat.avenginekit" to force usage (may lead to runtime failures)