🔥 Remove duplicate this.type = null assigment (#691)

At the moment in constructor we call
```js
this.type = null
```
twice. Let's remove one of the calls

Author: dawidreedsy

lib/client/doc.js

@@ -61,6 +61,7 @@ function Doc(connection, collection, id) {
   this.id = id;
 
   this.version = null;
+  // The OT type of this document. An uncreated document has type `null`
   this.type = null;
   this.data = undefined;
 
@@ -93,9 +94,6 @@ function Doc(connection, collection, id) {
   // This is a list of {[create:{...}], [del:true], [op:...], callbacks:[...]}
   this.pendingOps = [];
 
-  // The OT type of this document. An uncreated document has type `null`
-  this.type = null;
-
   // The applyStack enables us to track any ops submitted while we are
   // applying an op incrementally. This value is an array when we are
   // performing an incremental apply and null otherwise. When it is an array,