use shorter extension names #629

Job	Run time
Documentation	1m 17s
Julia 1.6 - ubuntu-latest - x64 - push	1m 49s
Julia 1.6 - windows-latest - x64 - push	8m 20s
Julia lts - ubuntu-latest - x64 - push	1m 56s
Julia lts - windows-latest - x64 - push	2m 32s
Julia 1 - ubuntu-latest - x64 - push	3m 7s
Julia 1 - windows-latest - x64 - push	4m 29s
Julia pre - ubuntu-latest - x64 - push	3m 0s
Julia pre - windows-latest - x64 - push	3m 44s
Julia nightly - ubuntu-latest - x64 - push	4m 19s
Julia nightly - windows-latest - x64 - push	5m 18s
	39m 51s

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