JS: Add missing qldoc

Author: asgerf

javascript/ql/lib/semmle/javascript/Modules.qll

@@ -129,6 +129,7 @@ abstract class Import extends AstNode {
   /** Gets the (unresolved) path that this import refers to. */
   abstract Expr getImportedPathExpr();
 
+  /** Gets the imported path as a string. */
   final string getImportedPathString() { result = this.getImportedPathExpr().getStringValue() }
 
   /**