ERROR: Missing main()

Hi.

I'm getting an error:

```
app.js:44688 THREE.WebGLProgram: shader error: 0 35715 false gl.getProgramInfoLog invalid shaders THREE.WebGLShader: gl.getShaderInfoLog() vertex
ERROR: Missing main()
```

Webpack rules:

```
webpack({
mode: "development",
output: {
filename: "app.js"
},
devtool: "source-map",
module: {
rules: [
{
test: /\.m?js$/,
exclude: /(node_modules|bower_components)/,
use: {
loader: "babel-loader",
options: {
presets: ["@babel/preset-env"]
}
}
},
{
test: /\.(glsl|vs|fs|vert|frag)$/,
exclude: /node_modules/,
use: [
'raw-loader',
'glslify-loader'
]
}
]
}
})
```

Shader files (.frag & .vert) are valid, because when I use them inline they work as expected. And they definitely have main functions.

Any ideas what am I doing wrong ?