Fix bug 1026623 - Set em:strictCompatibility to ensure the right Lightning version is used. r=ssitter

calendar/lightning/install.rdf

@@ -45,5 +45,6 @@
     <em:updateURL>@LIGHTNING_UPDATE_LOCATION@?buildID=@GRE_BUILDID@&amp;appABI=%APP_ABI%&amp;appOS=%APP_OS%&amp;locale=%APP_LOCALE%&amp;appVersion=%APP_VERSION%&amp;appID=%APP_ID%</em:updateURL>
 #endif
     <em:unpack>true</em:unpack>
+    <em:strictCompatibility>true</em:strictCompatibility>
   </Description>
 </RDF>