message: update package.xml, replate tab to 4-spaces.
diff: <email>shenzhe163@gmail.com</email>
  <active>yes</active>
  </developer>
  - <date>2017-03-17</date>
  + <date>2017-07-14</date>
  <time>09:50:10</time>
  <version>
  - <release>2.0.7</release>
  + <release>2.0.8</release>
  <api>2.0</api>
  </version>
  <stability>
  