Regenerate proto files (#1092)

The proto files in the current master are not compatible with the ones in dgraph.
See build for PR hypermodeinc/dgraph#4200
```
	[Step 3/5] # github.com/dgraph-io/dgraph/protos/pb
[11:02:11]	[Step 3/5] ../protos/pb/pb.pb.go:7146:29: m.Kv[iNdEx].MarshalToSizedBuffer undefined (type *pb.KV has no field or method MarshalToSizedBuffer)
[11:02:11]	[Step 3/5] ../protos/pb/pb.pb.go:7209:29: m.Kv[iNdEx].MarshalToSizedBuffer undefined (type *pb.KV has no field or method MarshalToSizedBuffer)
[11:02:40]	[Step 3/5] Makefile:66: recipe for target 'install' failed
[11:02:40]	[Step 3/5] make[1]: *** [install] Error 2
[11:02:40]	[Step 3/5] make[1]: Leaving directory '/home/pawan0201/go/src/github.com/dgraph-io/dgraph/dgraph'
[11:02:40]	[Step 3/5] make: *** [install] Error 2
[11:02:40]	[Step 3/5] Makefile:43: recipe for target 'install' failed
[11:02:40]	[Step 3/5] Process exited with code 2
```

https://teamcity.dgraph.io/viewLog.html?buildId=29232&buildTypeId=Dgraph_Blockade&tab=buildLog

This PR updates the proto files in badger. I've run `./gen.sh` script to regenerate these.