Fix linting error

src/app/files/fileManager.js

@@ -120,7 +120,7 @@ class FileManager extends Plugin {
    */
   exists (path) {
     const provider = this.fileProviderOf(path)
-    return provider ? true : false
+    return provider ? true : false // eslint-disable-line
   }
 
   /**
@@ -142,7 +142,7 @@ class FileManager extends Plugin {
   open (path) {
     this._handleExists(path, `Cannot open file ${path}`)
     this._handleIsFile(path, `Cannot open file ${path}`)
-    this.switchFile(path)
+    return this.switchFile(path)
   }
 
   /**