closure-templates at HEAD throws errors on any css

Create a template like this:

```
/**
* @param css
*/
{template .stylesheet}

{$css}

{/template}
```

call it

```
my.stylesheet({css: 'body { color: blue; }'})
```

Result: error:
AssertionError: Failure: Bad value `body { color: blue; }` for |filterCssValue
at new goog.asserts.AssertionError (/Users/nick/git/soynode/node_modules/obvious-closure-library/closure/goog/asserts/asserts.js:62:20)
at Object.goog.asserts.fail (/Users/nick/git/soynode/node_modules/obvious-closure-library/closure/goog/asserts/asserts.js:176:32)
at Object.soy.esc.$$filterCssValueHelper (/Users/nick/git/soynode/node_modules/closure-templates/soyutils_usegoog.js:2256:18)
at Object.soy.$$filterCssValue (/Users/nick/git/soynode/node_modules/closure-templates/soyutils_usegoog.js:1495:18)