theme/rana: use $OSTYPE instead of $(uname)

Author: gaelicWizard

themes/rana/rana.theme.bash

@@ -181,7 +181,7 @@ prompt() {
   local MOVE_CURSOR_RIGHTMOST='\033[500C'
   local MOVE_CURSOR_5_LEFT='\033[5D'
 
-  if [ $(uname) = "Linux" ];
+  if [[ "$OSTYPE" == 'linux'* ]];
   then
     PS1="${TITLEBAR}
 ${SAVE_CURSOR}${MOVE_CURSOR_RIGHTMOST}${MOVE_CURSOR_5_LEFT}\