Change "firmware version" to "android version"

Bug: 2391822
In Settings -> About phone, the platform version was under the label
"Firmware version".  That  doesn't really mean anything, because
the build number is a more accurate identifier for the build that
is currently running.
diff --git a/res/values/strings.xml b/res/values/strings.xml
index 3afe481..a680f04 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -1117,7 +1117,7 @@
     <string name="system_update_settings_list_item_summary">""</string>
 
     <!-- About phone screen, status item label -->
-    <string name="firmware_version">Firmware version</string>
+    <string name="firmware_version">Android version</string>
     <!-- About phone screen, status item label-->
     <string name="model_number">Model number</string>
     <!-- About phone screen,  setting option name-->