Fixes broken example in docs [(#987)](GoogleCloudPlatform/python-docs-samples#987)

Author: gguuss

samples/analyze/README.rst

@@ -89,7 +89,7 @@ To run this sample:
     Usage Examples:
     
         python analyze.py faces gs://demomaker/google_gmail.mp4
-        python analyze.py labels gs:/cloud-ml-sandbox/video/chicago.mp4
+        python analyze.py labels gs://cloud-ml-sandbox/video/chicago.mp4
         python analyze.py labels_file resources/cat.mp4
         python analyze.py shots gs://demomaker/gbikes_dinosaur.mp4
         python analyze.py safe_search gs://demomaker/gbikes_dinosaur.mp4

samples/analyze/analyze.py

@@ -20,7 +20,7 @@
 Usage Examples:
 
     python analyze.py faces gs://demomaker/google_gmail.mp4
-    python analyze.py labels gs:/cloud-ml-sandbox/video/chicago.mp4
+    python analyze.py labels gs://cloud-ml-sandbox/video/chicago.mp4
     python analyze.py labels_file resources/cat.mp4
     python analyze.py shots gs://demomaker/gbikes_dinosaur.mp4
     python analyze.py safe_search gs://demomaker/gbikes_dinosaur.mp4