Update Test Pilot version to 1.3.1 to match that uploaded to AMO. a=Standard8 DONTBUILD

mail/app/profile/extensions/tbtestpilot@labs.mozilla.com/install.rdf.in

@@ -6,7 +6,7 @@
      xmlns:em="http://www.mozilla.org/2004/em-rdf#">
   <Description about="urn:mozilla:install-manifest">
     <em:id>tbtestpilot@labs.mozilla.com</em:id>
-    <em:version>1.3</em:version>
+    <em:version>1.3.1</em:version>
     <em:type>2</em:type>
 
     <!-- Target Application this extension can install into,