zotero: 4.0.28 -> 4.0.29

Built and tested locally.

From the changelog:
```
Firefox 45/46 compatibility
* [Zotero Standalone] Save PDFs directly from browsers via the Save to
Zotero button
* Requires Chrome connector version 4.0.29; updated Safari connector
coming soon
* To convert a standalone PDF attachment to a full item, right-click
the item and choose “Retrieve Metadata for PDF” or “Create Parent
Item”.
* [Zotero for Firefox] Don't show Firefox open/save dialog when
showing style installation prompt
* Retry additional file sync failures automatically
* Fixed potential crash when dragging in files on some systems
* Fixed potential crash when dragging collections to another library
* Miscellaneous bibliographic output and word processor integration
fixes
* Updated citeproc-js to version 1.1.71
* Fixed spacing of toolbar icons on Windows/Linux in Firefox 43+
* Use larger text field for Book Title
* Make highlight color of selected items list rows on Linux more
distinct when items pane doesn't have focus
* [Zotero for Firefox] Improved error message on Firefox login manager
failure
* Improved error message when trying to use a later database version
```

pkgs/applications/office/zotero/default.nix

···
 
   xpi = fetchurl {
     url = "https://download.zotero.org/extension/zotero-${version}.xpi";
-    sha256 = "02h2ja08v8as4fawj683rh5rmxsjf5d0qmvqa77i176nm20y5s7s";
+    sha256 = "1dyf578yfj3xr9kkhmsvbkvraw2arghmh67ksi5c8qlxczx5i1xy";
   };
 
-  version = "4.0.28";
+  version = "4.0.29";
 
 in
 stdenv.mkDerivation {
···
   inherit version;
 
   src = fetchurl {
-    url = "https://github.com/zotero/zotero-standalone-build/archive/4.0.28.8.tar.gz";
-    sha256 = "ab1fd5dde9bd2a6b6d31cc9a53183a04de3698f1273a943ef31ecc4c42808a68";
+    url = "https://github.com/zotero/zotero-standalone-build/archive/4.0.29.2.tar.gz";
+    sha256 = "0pfip6s5dawp7wp8r5czvzlnxvvdwjja64g71h9dxyxrh49v2mxa";
   };
 
   nativeBuildInputs = [ perl unzipNLS ];