Fix hang when returning from shell command

In 5a3049485c we changed the execution of shell commands to use an interactive
shell (-i), because this allows users to use aliases or shell functions, which
is a nice convenience.

Since then, however, many users have reported problems with lazygit not coming
back to the foreground after executing a shell command. Some users report that
appending "; exit" to the end of the command line solves this. I don't really
understand what the cause of this problem was, or why appending "; exit" solves
it, but if it helps, let's do it.

pkg/commands/oscommands/os_windows.go

@@ -2,10 +2,11 @@ package oscommands
 
 func GetPlatform() *Platform {
 	return &Platform{
-		OS:                  "windows",
-		Shell:               "cmd",
-		InteractiveShell:    "cmd",
-		ShellArg:            "/c",
-		InteractiveShellArg: "",
+		OS:                   "windows",
+		Shell:                "cmd",
+		InteractiveShell:     "cmd",
+		ShellArg:             "/c",
+		InteractiveShellArg:  "",
+		InteractiveShellExit: "",
 	}
 }