Correctly check map location attr presence validations

spec/models/map_location_spec.rb

@@ -8,12 +8,13 @@ describe MapLocation do
     expect(map_location).to be_valid
   end
 
-  it "fails if longitude, latitude or zoom attributes are blank" do
+  it "is invalid when longitude/latitude/zoom are not present" do
     map_location.longitude = nil
     map_location.latitude = nil
+    map_location.zoom = nil
 
-    expect(map_location).to_not be_valid
-    expect(map_location.errors.size).to eq(2)
+    expect(map_location).not_to be_valid
+    expect(map_location.errors.size).to eq(3)
   end
 
   context "#available?" do