run tests with Julia 1.6 (Long-term support release) #54

Job	Run time
Julia 1.3 - ubuntu-latest - x64	1m 19s
Julia 1.3 - windows-latest - x64	5m 40s
Julia 1.3 - macOS-latest - x64	2m 44s
Julia 1.6 - ubuntu-latest - x64	37s
Julia 1.6 - windows-latest - x64	6m 41s
Julia 1.6 - macOS-latest - x64	1m 20s
Julia 1 - ubuntu-latest - x64	41s
Julia 1 - windows-latest - x64	55s
Julia 1 - macOS-latest - x64	53s
Julia nightly - ubuntu-latest - x64	54s
Julia nightly - windows-latest - x64	1m 16s
Julia nightly - macOS-latest - x64	1m 14s
	24m 14s

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