[ExcelAnalyzer] Add threshold for hidden rows

We've had no serious data breaches at this level and it would reduce the
number of hidden row hits by over half.

gems/excel_analyzer/lib/excel_analyzer/xlsx_analyzer.rb

@@ -45,6 +45,7 @@ def suspected_problem?(data)
       return false if total_count == 0
       return false if data[:named_ranges] == total_count
       return false if data[:external_links] == total_count
+      return false if data[:hidden_rows] == total_count && total_count <= 50
 
       true
     end

gems/excel_analyzer/spec/excel_analyzer/xlsx_analyzer_spec.rb

@@ -179,5 +179,21 @@
         expect(ExcelAnalyzer.on_hidden_metadata).to receive(:call)
       end
     end
+
+    context 'when metadata contains 50 hidden rows only' do
+      let(:metadata) { { hidden_rows: 50 } }
+
+      it 'should not be run' do
+        expect(ExcelAnalyzer.on_hidden_metadata).to_not receive(:call)
+      end
+    end
+
+    context 'when metadata contains 50 hidden rows and anything else' do
+      let(:metadata) { { hidden_rows: 50, other: 1 } }
+
+      it 'should run' do
+        expect(ExcelAnalyzer.on_hidden_metadata).to receive(:call)
+      end
+    end
   end
 end