Deps: Update robolectric to 4.9

This is done because otherwise the 'testDebugUnitTest' task fails the
test, when run on command line, with the below 'ClassNotFoundException'
error:

------------------------------------------------------------------------

java.lang.NoClassDefFoundError: android/content/ContentResolver
...
Caused by: java.lang.ClassNotFoundException:
couldn't load android.content.ContentResolver
...
Caused by: java.lang.IllegalArgumentException:
Unsupported class file major version 61"

------------------------------------------------------------------------

Release Link: https://github.com/robolectric/robolectric/releases/tag/
robolectric-4.9

build.gradle

@@ -61,7 +61,7 @@ ext {
     tagSoupVersion = '1.2.1'
     glideVersion = '4.10.0'
     picassoVersion = '2.5.2'
-    robolectricVersion = '4.4'
+    robolectricVersion = '4.9'
     jUnitVersion = '4.12'
     jSoupVersion = '1.11.3'
     wordpressUtilsVersion = 'trunk-1ed207c03d2242b6fc3d74f9e388e9163cbc82a6'