Fix not shown 'exception page' on non windows system

Occurs on non windows system where Environment.NewLine is LF (1 symbol length) Unix, Linux, OS X etc. And options.ShowExceptionDetails is true.
Replaced number '2' to Environment.NewLine.Length.
Handle IBuilder rename to IApplicationBuilder.
Reacting to System.Text.Encoding package version change
Updating release NuGet.config
Updating dev NuGet.config
Merge pull request #35 from turchenkoalex/bug-27

Issue #27: Error page middleware returns an empty body on OS X
Runtime information page