Make resolve a little cleaner, always throw error

Author: Ilya Radchenko

lib/resolve_theme.js

@@ -11,12 +11,12 @@ var path = require('path'),
  * @returns {string} directory
  */
 function resolveTheme(theme) {
-  if (!theme) {
-    return path.dirname(resolve.sync('documentation-theme-default', { basedir: __dirname }));
-  }
+  var basedir = theme ? process.cwd() : __dirname;
+  
+  theme = theme || 'documentation-theme-default';
 
   try {
-    return path.dirname(resolve.sync(theme, { basedir: process.cwd() }));
+    return path.dirname(resolve.sync(theme, { basedir: basedir }));
   } catch (e) {
     throw new Error('Theme ' + theme + ' not found');
   }