Fix posh-git PowerShell module loading

We simply need to call out that we want to load the post-git PowerShell module.
Caused by breaking change from the posh-git project: dahlbyk/posh-git#376

generator_files/cookbooks/workstation/templates/default/ise_profile.ps1.erb

@@ -1,5 +1,5 @@
-# Load posh-git example profile
-. '<%= @home %>\Documents\WindowsPowerShell\Modules\posh-git\profile.example.ps1'
+# Load posh-git
+Import-Module posh-git
 
 # Load PSReadline
 Import-Module PSReadLine