validate files: fix usage error in example command

visudo requires the -f option to check any other file than the default.
I've added this to the example ansible tasks.

files/copy

@@ -87,7 +87,7 @@ EXAMPLES = '''
 - copy: src=/mine/ntp.conf dest=/etc/ntp.conf owner=root group=root mode=644 backup=yes
 
 # Copy a new "sudoers" file into place, after passing validation with visudo
-- copy: src=/mine/sudoers dest=/etc/sudoers validate='visudo -c %s'
+- copy: src=/mine/sudoers dest=/etc/sudoers validate='visudo -cf %s'
 '''
 
 def main():

files/template

@@ -58,5 +58,5 @@ EXAMPLES = '''
 - template: src=/mytemplates/foo.j2 dest=/etc/file.conf owner=bin group=wheel mode=0644
 
 # Copy a new "sudoers file into place, after passing validation with visudo
-- action: template src=/mine/sudoers dest=/etc/sudoers validate='visudo -c %s'
+- action: template src=/mine/sudoers dest=/etc/sudoers validate='visudo -cf %s'
 '''