Allow latest version for MLVision on ios (#804)

Author: bparrishMines

packages/firebase_ml_vision/ios/firebase_ml_vision.podspec

@@ -17,11 +17,11 @@ An SDK that brings Google's machine learning expertise to Android and iOS apps i
   s.public_header_files = 'Classes/**/*.h'
   s.dependency 'Flutter'
   s.dependency 'Firebase/Core'
-  s.dependency 'Firebase/MLVision', '5.6.0'
-  s.dependency 'Firebase/MLVisionBarcodeModel', '5.6.0'
-  s.dependency 'Firebase/MLVisionFaceModel', '5.6.0'
-  s.dependency 'Firebase/MLVisionLabelModel', '5.6.0'
-  s.dependency 'Firebase/MLVisionTextModel', '5.6.0'
+  s.dependency 'Firebase/MLVision'
+  s.dependency 'Firebase/MLVisionBarcodeModel'
+  s.dependency 'Firebase/MLVisionFaceModel'
+  s.dependency 'Firebase/MLVisionLabelModel'
+  s.dependency 'Firebase/MLVisionTextModel'
   s.ios.deployment_target = '8.0'
   s.static_framework = true
 end