fixed cellHeight() check for no-op return

the code that checked for cell height and unit being the same was incorrect.

Testing Done:  calling this should be no-op, but wasn't
this.grid.cellHeight( this.grid.cellHeight() );

Author: adumesny

src/gridstack.js

@@ -1610,7 +1610,7 @@
         }
         var heightData = Utils.parseHeight(val);
 
-        if (this.opts.cellHeightUnit === heightData.heightUnit && this.opts.height === heightData.height) {
+        if (this.opts.cellHeightUnit === heightData.unit && this.opts.cellHeight === heightData.height) {
             return ;
         }
         this.opts.cellHeightUnit = heightData.unit;