sourceMap is an alias for .sourceMaps, cannot use both

**Webpack Version:**
1.10.x/2.x

**Babel Core Version**:
7.0.0-bridge.0

**Babel Loader Version**:
^8.0.4

**Please tell us about your environment:**
OSX 10.x

**Current behavior:**

```
Html Webpack Plugin:
Error: Child compilation failed:
Module build failed (from ./node_modules/_babel-loader@7.1.5@babel-loader/lib/index.js):
Error: .sourceMap is an alias for .sourceMaps, cannot use both
```