Convert window render sizes to floats

GLSL 1.10 is typesafe ([PDF specs](https://www.khronos.org/registry/OpenGL/specs/gl/GLSLangSpec.1.10.pdf), page 22), so this shader will not load properly during build.

It's not a super important change, but I came across it while playing with the examples on my pi.

examples/shaders/resources/shaders/glsl100/swirl.fs

@@ -13,8 +13,8 @@ uniform vec4 colDiffuse;
 // NOTE: Add here your custom variables
 
 // NOTE: Render size values should be passed from code
-const float renderWidth = 800;
-const float renderHeight = 450;
+const float renderWidth = 800.0;
+const float renderHeight = 450.0;
 
 float radius = 250.0;
 float angle = 0.8;
@@ -43,4 +43,4 @@ void main()
     vec4 color = texture2D(texture0, tc/texSize)*colDiffuse*fragColor;;
 
     gl_FragColor = vec4(color.rgb, 1.0);;
-}
+}