pre-commit: Use uname -a instead.

Not all shells support uname -o.

Change-Id: Ia6f46f3580f6d7b421da672418dcbee38ad9e60b
Reviewed-on: https://code.wireshark.org/review/14143
Reviewed-by: João Valverde <j@v6e.pt>

tools/pre-commit

@@ -19,10 +19,10 @@
 # If the commit identifier is not given, use HEAD instead.
 COMMIT_ID="${1:-HEAD}"
 
-UNAME=`uname -o`
+UNAME=`uname -a`
 
 case "$UNAME" in
-    Msys)
+    *\ Msys)
         pyvar="pythonw.exe"
         ;;
     *)