Update to PSReadLine 2.0.0-beta4 (#952)

Author: rjmholt

modules.json

@@ -10,7 +10,7 @@
         "AllowPrerelease":false
     },
     "PSReadLine":{
-        "MinimumVersion":"2.0.0-beta3",
+        "MinimumVersion":"2.0.0-beta4",
         "MaximumVersion":"2.1",
         "AllowPrerelease":true
     }

src/PowerShellEditorServices/Session/PSReadLinePromptContext.cs

@@ -32,7 +32,7 @@ internal class PSReadLinePromptContext : IPromptContext {
             end {
                 $module = Get-Module -ListAvailable PSReadLine |
                     Where-Object Version -eq '2.0.0' |
-                    Where-Object { $_.PrivateData.PSData.Prerelease -notin 'beta1','beta2' } |
+                    Where-Object { $_.PrivateData.PSData.Prerelease -notin 'beta1','beta2','beta3' } |
                     Sort-Object -Descending Version |
                     Select-Object -First 1
                 if (-not $module) {