Illegal reflection error compiling soy templates

When compiling a soy template using bazel 0.20.0 I get warnings like this:
```
INFO: From Generating 1 SOY v2 JS file(s):
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by com.google.inject.internal.cglib.core.$ReflectUtils$1 (file:/home/ribrdb/.cache/bazel/_bazel_ribrdb/a393754d6dfbc9daf01e7035f8b22381/external/com_google_inject_guice/guice-4.1.0.jar) to method java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain)
WARNING: Please consider reporting this to the maintainers of com.google.inject.internal.cglib.core.$ReflectUtils$1
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
```