Fix AutoLaunch for Linux AppImages (#126)

per Teamwork/node-auto-launch#89,
this resolves the desktop autostart path to the executable, which
defaulted to current working path of the running process. Due to the
AppImage architecture, that default doesn't work cleanly and requires
override.

src/AutoLauncher.js

@@ -1,13 +1,17 @@
 const settings = require('electron-settings')
 const AutoLaunch = require('auto-launch')
 const config = require('./config.json')
+const os = require('os');
 
 class AutoLauncher {
   constructor () {
     const autoLaunchOpts = {
       name: 'Stethoscope',
       isHidden: true
     }
+    if (os.platform() === 'linux' && process.env.APPIMAGE) {
+      autoLaunchOpts.path = process.env.APPIMAGE
+    }
     this.stethoscopeAutoLauncher = new AutoLaunch(autoLaunchOpts)
   }