Add offsetToZero to gfunc.

src/app/services/graphite/gfunc.js

@@ -328,6 +328,11 @@ function (_) {
     defaultParams: [10]
   });
 
+  addFuncDef({
+    name: 'offsetToZero',
+    category: categories.Transform,
+  });
+
   addFuncDef({
     name: 'transformNull',
     category: categories.Transform,