functions as type definitions not highlighting correctly

https://github.com/fsharp/emacs-fsharp-mode/blob/96513ea53b51dd5abc32c0a0d5b1443484e367be/fsharp-mode-font.el#L77

``` fsharp
static member FMapC2 (f: float -> float -> float) (c1, c2) =
{r=f c1.r c2.r; g = f c1.g c2.g; b = f c1.b c2.b}
```

Type definitions of functions are not highlighted properly in emacs. Arrows are correct however subsequent types after arrows are left unhighlighted. I believe that line 77 in fsharp-mode-font.el is to blame.