Ensure falsey root value doesn't get passed to postcss-import

Author: simonsmith

lib/index.js

@@ -91,7 +91,9 @@ function mergeOptions(options) {
   var merged = assign({}, defaults, options);
 
   // Set some core options
-  merged['postcss-import'].root = merged.root;
+  if (merged.root) {
+    merged['postcss-import'].root = merged.root;
+  }
 
   // Call beforeLint function and pass processed css to bem-linter
   var beforeLint = merged.beforeLint;