webpack 5 support

**Describe the bug**
When installing in a project that uses webpack 5 (e.g. STAC Browser), I'm getting the following error when running `npm install`:

```
Could not resolve dependency:
npm WARN peer webpack@"^3.0.0 || ^4.0.0-alpha.0 || ^4.0.0" from worker-loader@2.0.0
npm WARN node_modules/worker-loader
npm WARN worker-loader@"^2.0.0" from georaster@1.5.6
npm WARN node_modules/georaster
npm WARN
npm WARN Conflicting peer dependency: webpack@4.46.0
npm WARN node_modules/webpack
npm WARN peer webpack@"^3.0.0 || ^4.0.0-alpha.0 || ^4.0.0" from worker-loader@2.0.0
npm WARN node_modules/worker-loader
npm WARN worker-loader@"^2.0.0" from georaster@1.5.6
npm WARN node_modules/georaster
```

**Expected behavior**
Could we allow webpack 5, too?