Undocumented raw-loader bug

I noticed what appears to be a bug when using this syntax:

```js
import vertexShade from 'raw-loader!glslify-loader!./VertexShader.vert'
console.log(vertexShader)
```

would print
```js
#define GLSLIFY 1
export default "#define GLSLIFY 1\nvarying vec2 vUv;\nvoid main() {\n vUv = uv;\n gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );\n}";
```

Notice that it includes `#define GLSLIFY 1` twice, and `export default` which makes it invalid GLSL. This would cause the shader compilation to fail.

Here is my webpack config:

```js
rules: [
{
test: /\.(glsl|vs|fs|vert|frag)$/,
exclude: /node_modules/,
use: [
'raw-loader',
'glslify-loader'
]
},
]
```

### The Solution

I came across this in the documentation for raw-loader:

```
Beware, if you already define loader(s) for extension(s) in webpack.config.js you should use:

import css from '!!raw-loader!./file.txt'; // Adding `!!` to a request will disable all loaders specified in the configuration
```

When I added it to my code, it worked properly.

```js
import vertexShader from '!!raw-loader!glslify-loader!./VertexShader.vert'
console.log(vertexShader)
```
now prints:

```
#define GLSLIFY 1
varying vec2 vUv;
void main() {
vUv = uv;
gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );
}
```
Now the shader compiles successfully. Not sure if this was an issue in my configuration somehow, and I'm not sure what to title this issue, but hope it helps someone.