Updated NSQ and made changes to stats parsing for the new version

[mjiori]

Upgrades NSQ 1.2.0 -> 1.3.0

Ingest completed successfully in interactive mode. The only breaking changes found were related to a new data structure for stats reporting, which is fixed in this PR.

[diamondap]

This has one failing test in the end-to-end tests.

--- FAIL: TestEndToEnd (0.20s)
    helpers_test.go:183:
        	Error Trace:	/Users/diamond/aptrust/preservation-services/e2e/helpers_test.go:183
        	            				/Users/diamond/aptrust/preservation-services/e2e/helpers_test.go:155
        	            				/Users/diamond/aptrust/preservation-services/e2e/helpers_test.go:68
        	            				/Users/diamond/aptrust/preservation-services/e2e/e2e_test.go:55
        	            				/Users/diamond/aptrust/preservation-services/e2e/e2e_test.go:42
        	Error:      	Expected nil, but got: &json.UnmarshalTypeError{Value:"object", Type:(*reflect.rtype)(0x102fa3e20), Offset:299, Struct:"ChannelStats", Field:"topics.channels.clients"}
        	Test:       	TestEndToEnd

[mjiori]

I was able to fix the failing test issue by pulling in the new data structures from NSQ 1.3 into our NSQClient. Not ideal because we'll need to make changes to our client every time we update NSQ, but it will address the issue.

All tests passing.

[diamondap]

This looks good. Feel free to merge when appropriate.