chore: add blacken to template

Source-Author: Leah E. Cole <6719667+leahecole@users.noreply.github.com>
Source-Date: Thu Nov 5 15:22:03 2020 -0800
Source-Repo: googleapis/synthtool
Source-Sha: 1f1148d3c7a7a52f0c98077f976bd9b3c948ee2b
Source-Link: googleapis/synthtool@1f1148d

samples/snippets/noxfile.py

@@ -148,7 +148,16 @@ def lint(session):
         "."
     ]
     session.run("flake8", *args)
+#
+# Black
+#
+
+@nox.session
+def blacken(session):
+    session.install("black")
+    python_files = [path for path in os.listdir(".") if path.endswith(".py")]
 
+    session.run("black", *python_files)
 
 #
 # Sample Tests

synth.metadata

@@ -19,14 +19,14 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "3d3e94c4e02370f307a9a200b0c743c3d8d19f29"
+        "sha": "1f1148d3c7a7a52f0c98077f976bd9b3c948ee2b"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "3d3e94c4e02370f307a9a200b0c743c3d8d19f29"
+        "sha": "1f1148d3c7a7a52f0c98077f976bd9b3c948ee2b"
       }
     }
   ],