Fix incorrect license information of pom

[chibatching]

Twitter Kit for Android is licensed under Apache Licenses 2.0. But pom file indicate that TwitterKit Agreement licenses.

  <licenses>
    <license>
      <name>TwitterKit Agreement</name>
      <url>https://dev.twitter.com/overview/terms/twitterkit.html</url>
      <distribution>repo</distribution>
    </license>
  </licenses>

I'm not sure how pom file is genarated in this project. But I found incorrect information in gradle.properites, and fix it.

[CLAassistant]

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