Fix: syncImport issue #1389 (nodejs)

lib/less/env.js

@@ -10,6 +10,7 @@
         'dumpLineNumbers',  // option - whether to dump line numbers
         'compress',         // option - whether to compress
         'processImports',   // option - whether to process imports. if false then imports will not be imported
+        'syncImport',       // option - whether to import synchronously
         'mime',             // browser only - mime type for sheet import
         'currentFileInfo'   // information about the current file - for error reporting and importing and making urls relative etc.
     ];