Proguard R8 needs an update

**Proguard file needs an update:**

The current version of R8 implicitly keeps the default constructor for Proguard configuration rules that have no member pattern. If the following rule should continue to keep the default constructor in the next major version of R8, then it must be augmented with the member pattern `{ void (); }` to explicitly keep the default constructor:
-keep public class * implements com.bumptech.glide.module.GlideModule

**Should be:**
```
-keep public class * implements com.bumptech.glide.module.GlideModule {
(...);
}
```

**Is:**
`-keep public class * implements com.bumptech.glide.module.GlideModule`

**File:**
https://github.com/bumptech/glide/blob/master/library/proguard-rules.txt