Set the sky colour to blue

Addresses issue #11
I think we should run an A/B test.

> On Jul 25, 2014, at 2:55 PM, Clark Gaebel <notifications@github.com> wrote:
> 
> In src/main.rs:
> 
> > @@ -46,6 +46,8 @@ static MAX_WORLD_SIZE: uint = 20000;
> >  
> >  static MAX_JUMP_FUEL: uint = 4;
> >  
> > +static SKY_COLOR: Color4<GLfloat>  = Color4 {r: 0.2, g: 0.5, b: 0.7, a: 1.0 };
> These values seem off. Can you make a powerpoint presentation with graphs and combinational decision making to pick more optimal ones?
> 
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