CompatHelper: bump compat for Rmath to 0.8, (keep existing compat) #225

Job	Run time
Documentation	3m 2s
Julia 1.3 - ubuntu-latest - x64 - pull_request	3m 30s
Julia 1.3 - macOS-latest - x64 - pull_request	4m 27s
Julia 1.3 - windows-latest - x64 - pull_request	13m 34s
Julia 1 - ubuntu-latest - x64 - pull_request	3m 46s
Julia 1 - macOS-latest - x64 - pull_request	4m 31s
Julia 1 - windows-latest - x64 - pull_request	4m 27s
Julia nightly - ubuntu-latest - x64 - pull_request	2m 3s
Julia nightly - macOS-latest - x64 - pull_request	3m 8s
Julia nightly - windows-latest - x64 - pull_request	3m 10s
	45m 38s

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