The next path separator fix hack for Linux NuGet installs

[BruceHaley]

#1872

This is pending someone from support verifying the generated NuGet package installs on a Mac.

Example: Microsoft.Bot.Builder 4.5.0-preview-190620-16

[coveralls]

Pull Request Test Coverage Report for Build 66359

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 71.942%

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Totals
Change from base Build 66092:	0.0%
Covered Lines:	4528
Relevant Lines:	6294

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💛 - Coveralls

[fuselabs]

✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.AI.Luis.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.AI.QnA.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.ApplicationInsights.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.Azure.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.Dialogs.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.TemplateManager.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Configuration.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Connector.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Schema.dll compared against version 4.3.1

[tomlm]