fix: preserve exit code in .cmd files

Because we're now exiting with an explicit exit command, we have to
preserve %errorlevel% (the equivalent of $? in bash).

index.js

@@ -113,7 +113,7 @@ function writeShim_ (from, to, prog, args, variables, cb) {
   //
   // "%_prog%" "%dp0%\.\node_modules\npm\bin\npm-cli.js" %*
   // @ENDLOCAL
-  // @EXIT /b
+  // @EXIT /b %errorlevel%
   //
   // :find_dp0
   // SET dp0=%~dp0
@@ -124,7 +124,7 @@ function writeShim_ (from, to, prog, args, variables, cb) {
     'SETLOCAL\r\n' +
     'CALL :find_dp0\r\n'
   var foot = 'ENDLOCAL\r\n' +
-    'EXIT /b\r\n' +
+    'EXIT /b %errorlevel%\r\n' +
     ':find_dp0\r\n' +
     'SET dp0=%~dp0\r\n' +
     'EXIT /b\r\n'

tap-snapshots/test-basic.js-TAP.test.js

@@ -19,7 +19,7 @@ IF EXIST "%dp0%\\node.exe" (\\r
 \\r
 "%_prog%"  "%dp0%\\from.env" %*\\r
 ENDLOCAL\\r
-EXIT /b\\r
+EXIT /b %errorlevel%\\r
 :find_dp0\\r
 SET dp0=%~dp0\\r
 EXIT /b\\r
@@ -81,7 +81,7 @@ IF EXIST "%dp0%\\node.exe" (\\r
 \\r
 "%_prog%" --expose_gc "%dp0%\\from.env.args" %*\\r
 ENDLOCAL\\r
-EXIT /b\\r
+EXIT /b %errorlevel%\\r
 :find_dp0\\r
 SET dp0=%~dp0\\r
 EXIT /b\\r
@@ -144,7 +144,7 @@ IF EXIST "%dp0%\\node.exe" (\\r
 \\r
 "%_prog%"  "%dp0%\\from.env.variables" %*\\r
 ENDLOCAL\\r
-EXIT /b\\r
+EXIT /b %errorlevel%\\r
 :find_dp0\\r
 SET dp0=%~dp0\\r
 EXIT /b\\r
@@ -206,7 +206,7 @@ IF EXIST "%dp0%\\/usr/bin/sh.exe" (\\r
 \\r
 "%_prog%"  "%dp0%\\from.sh" %*\\r
 ENDLOCAL\\r
-EXIT /b\\r
+EXIT /b %errorlevel%\\r
 :find_dp0\\r
 SET dp0=%~dp0\\r
 EXIT /b\\r
@@ -268,7 +268,7 @@ IF EXIST "%dp0%\\/usr/bin/sh.exe" (\\r
 \\r
 "%_prog%" -x "%dp0%\\from.sh.args" %*\\r
 ENDLOCAL\\r
-EXIT /b\\r
+EXIT /b %errorlevel%\\r
 :find_dp0\\r
 SET dp0=%~dp0\\r
 EXIT /b\\r
@@ -322,7 +322,7 @@ SETLOCAL\\r
 CALL :find_dp0\\r
 "%dp0%\\from.exe"   %*\\r
 ENDLOCAL\\r
-EXIT /b\\r
+EXIT /b %errorlevel%\\r
 :find_dp0\\r
 SET dp0=%~dp0\\r
 EXIT /b\\r
@@ -363,7 +363,7 @@ SETLOCAL\\r
 CALL :find_dp0\\r
 "%dp0%\\"   %*\\r
 ENDLOCAL\\r
-EXIT /b\\r
+EXIT /b %errorlevel%\\r
 :find_dp0\\r
 SET dp0=%~dp0\\r
 EXIT /b\\r
@@ -404,7 +404,7 @@ SETLOCAL\\r
 CALL :find_dp0\\r
 "%dp0%\\from.exe"   %*\\r
 ENDLOCAL\\r
-EXIT /b\\r
+EXIT /b %errorlevel%\\r
 :find_dp0\\r
 SET dp0=%~dp0\\r
 EXIT /b\\r