Update dev.ps1

Author: Kriechi

dev.ps1

@@ -1,8 +1,8 @@
 $ErrorActionPreference = "Stop"
 
 $pyver = python --version
-if($pyver -notmatch "3\.[5-9]") {
-    Write-Warning "Unexpected Python version, expected Python 3.5 or above: $pyver"
+if($pyver -notmatch "3\.[6-9]") {
+    Write-Warning "Unexpected Python version, expected Python 3.6 or above: $pyver"
 }
 
 python -m venv .\venv --copies
@@ -17,4 +17,4 @@ echo @"
   * Installed all dependencies into the virtualenv.
   * Activated virtualenv environment.
 
-"@
+"@