Return str in describe() as said by the blurb.

utils/update_build_version.py

@@ -57,13 +57,18 @@ def describe(dir):
     Runs 'git describe', or alternately 'git rev-parse HEAD', in dir.  If
     successful, returns the output; otherwise returns 'unknown hash, <date>'."""
     try:
-        return command_output(['git', 'describe'], dir).rstrip()
+        # decode() is needed here for Python3 compatibility. In Python2,
+        # str and bytes are the same type, but not in Python3.
+        # Popen.communicate() returns a bytes instance, which needs to be
+        # decoded into text data first in Python3. And this decode() won't
+        # hurt Python2.
+        return command_output(['git', 'describe'], dir).rstrip().decode()
     except:
         try:
-            return command_output(['git', 'rev-parse', 'HEAD'], dir).rstrip()
+            return command_output(
+                ['git', 'rev-parse', 'HEAD'], dir).rstrip().decode()
         except:
-            return 'unknown hash, {}'.format(
-                datetime.date.today().isoformat()).encode('ascii')
+            return 'unknown hash, {}'.format(datetime.date.today().isoformat())
 
 
 def main():
@@ -72,12 +77,7 @@ def main():
         sys.exit(1)
 
     new_content = '"spirv-tools {}\\n"\n'.format(
-        # decode() is needed here for Python3 compatibility. In Python2,
-        # str and bytes are the same type, but not in Python3.
-        # Popen.communicate() returns a bytes instance, which needs to be
-        # decoded into text data first in Python3. And this decode() won't
-        # hurt Python2.
-        describe(sys.argv[1]).decode('ascii').replace('"', '\\"'))
+        describe(sys.argv[1]).replace('"', '\\"'))
     if os.path.isfile(OUTFILE) and new_content == open(OUTFILE, 'r').read():
         sys.exit(0)
     open(OUTFILE, 'w').write(new_content)