assemble_maven doesn't know how to package exports

[anuragagarwal561994]

The line below creates issue for exports since this is not handled while packaging:

bazel-distribution/maven/rules.bzl

Line 211 in 3729c30

fail("Unsure how to package dependency for target: %s" % target)

An example where this breaks is @io_grpc_grpc_java//stub:javax_annotation

https://github.com/grpc/grpc-java/blob/master/stub/BUILD.bazel

Here I get the above error:

fail("Unsure how to package dependency for target: %s" % target)

and hence I am not able to assemble jars which require building grpc.