Fix Travis handling of a fully-numeric commit hash being YAML-converted to a number instead of a string

Docker-DCO-1.0-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)

hack/travis/dco.py

@@ -5,7 +5,7 @@ import yaml
 
 from env import commit_range
 
-commit_format = '-%n hash: %h%n author: %aN <%aE>%n message: |%n%w(0,2,2)%B'
+commit_format = '-%n hash: "%h"%n author: %aN <%aE>%n message: |%n%w(0,2,2)%B'
 
 gitlog = subprocess.check_output([
 	'git', 'log', '--reverse',