Invalid text render

``` js
var canvas = new Canvas(600, 600),
ctx = canvas.getContext('2d');

ctx.font = '30px Impact';
ctx.fillText("12", 100, 300);

var stream = canvas.pngStream();
```

Output of pngStream:


System info:
- canvas: 1.2.1
- pixman: stable 0.32.6 (bottled)
- cairo: stable 1.14.2 (bottled)
==> Dependencies
Build: xz ✔, pkg-config ✔
Required: freetype ✔, fontconfig ✔, libpng ✔, pixman ✔, glib ✔
==> Options
--universal
Build a universal binary
--without-x11
Build without x11 support
- fontconfig: stable 2.11.1 (bottled)
- freetype: stable 2.5.5 (bottled)
- glib: stable 2.44.0 (bottled)
- uname: Darwin 14.1.0 Darwin Kernel Version 14.1.0: Thu Feb 26 19:26:47 PST 2015; root:xnu-2782.10.73~1/RELEASE_X86_64 x86_64
- node -v: v0.10.38, v0.12.2