Improve identification of WSL (#196)

Ignore case when searching for Microsoft inside /proc/version.

yadm

@@ -1524,6 +1524,13 @@ function configure_repo() {
 
 function set_operating_system() {
 
+  # setting nocasematch to ignore case
+  local unset_nocasematch
+  if ! shopt nocasematch &> /dev/null; then
+    unset_nocasematch=1
+  fi
+  shopt -s nocasematch &> /dev/null
+
   # special detection of WSL (windows subsystem for linux)
   local proc_version
   proc_version=$(cat "$PROC_VERSION" 2>/dev/null)
@@ -1545,6 +1552,10 @@ function set_operating_system() {
       ;;
   esac
 
+  if [ "$unset_nocasematch" = "1" ]; then
+    shopt -u nocasematch &> /dev/null
+  fi
+
 }
 
 function set_awk() {