Bump Go version used to build BAAS

[rorbech]

This PR bumps the version to meet requirement of latest BaaS versions (https://github.com/10gen/baas/blob/master/etc/docs/onboarding.md#go)

What, How & Why?

☑️ ToDos

• [ ] 📝 Changelog update
• [ ] 🚦 Tests (or not relevant)
• [ ] C-API, if public C++ API changed.

[coveralls-official]

Pull Request Test Coverage Report for Build github_pull_request_282419

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 143 unchanged lines in 14 files lost coverage.
• Overall coverage decreased (-0.04%) to 91.637%

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Files with Coverage Reduction	New Missed Lines	%
src/realm/index_string.cpp	1	87.81%
src/realm/sync/network/network.cpp	1	89.65%
src/realm/sync/network/http.hpp	2	80.87%
src/realm/sync/noinst/server/server_history.cpp	2	67.69%
src/realm/alloc_slab.cpp	5	92.89%
src/realm/sync/network/default_socket.cpp	5	74.36%
src/realm/bplustree.cpp	6	76.91%
src/realm/sync/network/network.hpp	7	85.41%
src/realm/sync/noinst/protocol_codec.hpp	7	76.05%
test/sync_fixtures.hpp	7	76.57%

Totals
Change from base Build 1807:	-0.04%
Covered Lines:	230736
Relevant Lines:	251793

---

💛 - Coveralls

[danieltabacaru]

This PR bumps the Go version.