Dropping umbrella package from nox docs sessions.

Follow up to googleapis#3828.

Author: dhermes

docs/conf.py

@@ -70,7 +70,7 @@
 # built documents.
 #
 # The short X.Y version.
-distro = pkg_resources.get_distribution('google-cloud')
+distro = pkg_resources.get_distribution('google-cloud-core')
 release = os.getenv('SPHINX_RELEASE', distro.version)
 
 # The language for content autogenerated by Sphinx. Refer to documentation

nox.py

@@ -30,12 +30,25 @@ def docs(session):
     # Install Sphinx and also all of the google-cloud-* packages.
     session.chdir(os.path.realpath(os.path.dirname(__file__)))
     session.install('Sphinx >= 1.6.2', 'sphinx_rtd_theme')
-    session.install('.')
     session.install(
-        'core/', 'storage/', 'bigquery/', 'bigtable/', 'datastore/', 'dns/',
-        'language/', 'logging/', 'error_reporting/', 'monitoring/', 'pubsub/',
-        'resource_manager/', 'runtimeconfig/', 'spanner/', 'speech/',
-        'trace/', 'translate/', 'vision/',
+        'core/',
+        'storage/',
+        'bigquery/',
+        'bigtable/',
+        'datastore/',
+        'dns/',
+        'language/',
+        'logging/',
+        'error_reporting/',
+        'monitoring/',
+        'pubsub/',
+        'resource_manager/',
+        'runtimeconfig/',
+        'spanner/',
+        'speech/',
+        'trace/',
+        'translate/',
+        'vision/',
     )
 
     # Build the docs!