For PSV2.0 compat don't use $PSScriptRoot

As the build script must be executed from the `<projectroot>/scripts`
directory anyway we can assume `util.ps1` is as the same path as
`build.ps1` and just reference the current folder.

scripts/build.ps1

@@ -53,7 +53,8 @@ Param(
     [switch]$Compile
 )
 
-. "$PSScriptRoot\utils.ps1"
+# Dot source util functions into this scope
+. ".\utils.ps1"
 $ErrorActionPreference = "Stop"
 
 Push-Location -Path $saveTo