Refactor: use better variable name when determine to use winpty

Author: thetrompf

bin/yarn

@@ -1,19 +1,19 @@
 #!/bin/sh
 basedir=$(dirname "$(readlink "$0" || echo "$(echo "$0" | sed -e 's,\\,/,g')")")
 
-is_msys=0
+use_winpty=0
 
 case `uname` in
   *CYGWIN*) basedir=`cygpath -w "$basedir"`;;
-  MSYS_NT*|MINGW*) is_msys=1;;
+  MSYS_NT*) use_winpty=1;;
 esac
 
 command_exists() {
   command -v "$1" >/dev/null 2>&1;
 }
 
 if command_exists node; then
-  if [ $is_msys -eq 1 ]; then
+  if [ $use_winpty -eq 1 ]; then
     winpty node "$basedir/yarn.js" "$@"
   else
     node "$basedir/yarn.js" "$@"