opened
soufal
username_0
[Enter steps to reproduce:]

1. ...
2. ...

**Atom**: 1.29.0 x64
**Electron**: 2.0.5
**OS**: Unknown Windows version
**Thrown From**: [markdown-scroll-sync](https://github.com/mark-hahn/markdown-scroll-sync) package 2.1.2


### Stack Trace

Failed to activate the markdown-scroll-sync package

```
At Right-hand side of 'instanceof' is not callable

TypeError: Right-hand side of 'instanceof' is not callable
    at /packages/markdown-scroll-sync/lib/main.coffee:38:14
    at Workspace.observeActivePaneItem (~/AppData/Local/atom/app-1.29.0/resources/app/src/workspace.js:718:11)
    at MarkdownScrlSync.activate (/packages/markdown-scroll-sync/lib/main.coffee:25:30)
    at Package.activateNow (~/AppData/Local/atom/app-1.29.0/resources/app/src/package.js:230:33)
    at measure (~/AppData/Local/atom/app-1.29.0/resources/app/src/package.js:206:33)
    at Package.measure (~/AppData/Local/atom/app-1.29.0/resources/app/src/package.js:88:25)
    at activationPromise.Promise (~/AppData/Local/atom/app-1.29.0/resources/app/src/package.js:200:20)
    at new Promise (<anonymous>)
    at Package.activate (~/AppData/Local/atom/app-1.29.0/resources/app/src/package.js:198:38)
    at PackageManager.activatePackage (~/AppData/Local/atom/app-1.29.0/resources/app/src/package-manager.js:695:42)
    at config.transactAsync (~/AppData/Local/atom/app-1.29.0/resources/app/src/package-manager.js:670:36)
    at Config.transactAsync (~/AppData/Local/atom/app-1.29.0/resources/app/src/config.js:866:28)
    at PackageManager.activatePackages (~/AppData/Local/atom/app-1.29.0/resources/app/src/package-manager.js:668:23)
    at PackageManager.activate (~/AppData/Local/atom/app-1.29.0/resources/app/src/package-manager.js:647:50)
    at loadStatePromise.loadState.then (~/AppData/Local/atom/app-1.29.0/resources/app/src/atom-environment.js:871:27)
    at <anonymous>
```

### Commands

```
```

### Non-Core Packages

```
markdown-image-paste 2.5.2 
markdown-preview-plus 3.5.0 
markdown-scroll-sync 2.1.2 
markdown-themeable-pdf 1.2.1 
```
Failed to activate the markdown-scroll-sync package
issue