Merge pull request #37 from tmeinlschmidt/master

fixes 'derivate' function name - correct name is 'derivative'

src/app/services/graphite/gfunc.js

@@ -138,7 +138,7 @@ function (_) {
   });
 
   addFuncDef({
-    name: 'derivate',
+    name: 'derivative',
     category: categories.Transform,
   });
 
@@ -229,4 +229,4 @@ function (_) {
     }
   };
 
-});
\ No newline at end of file
+});