Bump the MSI version to 3.1, since the VS2015 redist requires it

* 3.1 is still available everywhere we care about - I think even 4.5
  ships with win7.

Author: baldurk

scripts/installer/Installer32.wxs

@@ -5,7 +5,7 @@
 
     <Package Id='*' Keywords='Installer' Description="Installer for RenderDoc"
       Comments='RenderDoc Homepage is http://renderdoc.org/' Manufacturer='Baldur Karlsson'
-      InstallerVersion='300' Languages='1033' Compressed='yes' SummaryCodepage='1252' />
+      InstallerVersion='301' Languages='1033' Compressed='yes' SummaryCodepage='1252' />
 
     <UI> 
        <Error Id="25000">Please use the 64-bit installer</Error> 

scripts/installer/Installer64.wxs

@@ -5,7 +5,7 @@
 
     <Package Id='*' Keywords='Installer' Description="Installer for RenderDoc"
       Comments='RenderDoc Homepage is http://renderdoc.org/' Platform="x64" Manufacturer='Baldur Karlsson'
-      InstallerVersion='300' Languages='1033' Compressed='yes' SummaryCodepage='1252' />
+      InstallerVersion='301' Languages='1033' Compressed='yes' SummaryCodepage='1252' />
 
     <InstallExecuteSequence>
       <RemoveExistingProducts After="InstallInitialize"/>