Make factory generate a valid SubmissionEntry

Without data, a SubmissionEntry will fail validation. Adds source as
well, just for good measure.

Author: tekin

spec/factories/submission_entry.rb

@@ -2,7 +2,7 @@
   factory :submission_entry do
     submission
     submission_file
-    data {}
-    source {}
+    data(test_key: 'some data')
+    source(sheet: 'InvoicesReceived', row: 1)
   end
 end