Update preview suffix

Author: Rob Holt

PowerShellEditorServices.Common.props

@@ -1,7 +1,7 @@
 <Project>
   <PropertyGroup>
     <VersionPrefix>2.0.0</VersionPrefix>
-    <VersionSuffix>preview.6</VersionSuffix>
+    <VersionSuffix>preview.7</VersionSuffix>
     <Company>Microsoft</Company>
     <Copyright>© Microsoft Corporation. All rights reserved.</Copyright>
     <PackageTags>PowerShell;editor;development;language;debugging</PackageTags>