fix changelog version and module version check

New regex doesn't check for a valid date next to the version.
This allows for a version to be specified with an "unreleased" date.

tests/Manifest.tests.ps1

@@ -56,7 +56,7 @@ Describe 'Module manifest' {
         $script:changelogVersion = $null
         It 'has a valid version in the changelog' {
             foreach ($line in (Get-Content $changelogPath)) {
-                if ($line -match "^## \[(?<Version>(\d+\.){1,3}\d+)\] \d{4}-\d{2}-\d{2}") {
+                if ($line -match "^##\s\[(?<Version>(\d+\.){1,3}\d+)\]") {
                     $script:changelogVersion = $matches.Version
                     break
                 }