Fixes for Cygwin

- Update install script to download Windows binary if $TERM == cygwin
- Unset TERM if $TERM == cygwin (#933)
- Always use cmd.exe instead of $SHELL when running commands

src/util/util_windows.go

@@ -12,15 +12,11 @@ import (
 
 // ExecCommand executes the given command with $SHELL
 func ExecCommand(command string) *exec.Cmd {
-	shell := os.Getenv("SHELL")
-	if len(shell) == 0 {
-		shell = "cmd"
-	}
 	args, _ := shellwords.Parse(command)
 	allArgs := make([]string, len(args)+1)
 	allArgs[0] = "/c"
 	copy(allArgs[1:], args)
-	return exec.Command(shell, allArgs...)
+	return exec.Command("cmd", allArgs...)
 }
 
 // IsWindows returns true on Windows