Correct cmake syntax in formula template

Closes Homebrew/homebrew#8879.

Signed-off-by: Charlie Sharpsteen <source@sharpsteen.net>

Library/Homebrew/cmd/create.rb

@@ -104,9 +104,9 @@ class FormulaCreator
       md5 '#{md5}'
 
     <% if mode == :cmake %>
-      depends_on 'cmake'
+      depends_on 'cmake' => :build
     <% elsif mode == nil %>
-      # depends_on 'cmake'
+      # depends_on 'cmake' => :build
     <% end %>
 
       def install