Add `minify.removeGlslifyDefinition` option

Removes the #define GLSLIFY 1 line at the beginning of each file.

v1.1.1...v1.2.0

Fix typo

• Fix typo b3c44d8

v1.1.0...v1.1.1

Flag uniform name collision with function parameter

• Flag uniform name collision eb94844 (See issue: leosingleton/webpack-glsl-minify#19)