Prevent Proguard from stripping interface info from @JsonAdapter classes
Prevent Proguard from stripping interface info from @JsonAdapter classes

Previously after Proguard, the classes would no longer implement the interfaces, leading to `JsonAdapterAnnotationTypeAdapterFactory` throwing.

Fixes #925
DanySK/gson-extras,DanySK/gson-extras,todoooo/gson,google/gson,DanySK/gson-extras,todoooo/gson,todoooo/gson