feat: warn on passing in unknown commands

bin/probot.js

@@ -1,6 +1,7 @@
 #!/usr/bin/env node
 
 const semver = require('semver')
+const program = require('commander')
 const version = require('../package').engines.node
 
 if (!semver.satisfies(process.version, version)) {
@@ -8,9 +9,16 @@ if (!semver.satisfies(process.version, version)) {
   process.exit(1)
 }
 
-require('commander')
+program
   .version(require('../package').version)
   .usage('<command> [options]')
   .command('run', 'run the bot')
   .command('receive', 'Receive a single event and payload')
+
+program.on('command:*', (cmd) => {
+  console.log(`\nInvalid command ${cmd}\n`)
+  program.outputHelp()  
+})
+
+program
   .parse(process.argv)