Update README & CONTRIBUTING

Fix broken links for Dev Chat that point to broken gitter.im room.
Remove lines about `mage vendor` target that is no longer available.
Remove broken table of contents links for headings in CONTRIBUTING.md
Fix typo

CONTRIBUTING.md

@@ -18,11 +18,8 @@ The Hugo community and maintainers are [very active](https://github.com/gohugoio
 * [Submitting Patches](#submitting-patches)
   * [Code Contribution Guidelines](#code-contribution-guidelines)
   * [Git Commit Message Guidelines](#git-commit-message-guidelines)
-  * [Vendored Dependencies](#vendored-dependencies)
   * [Fetching the Sources From GitHub](#fetching-the-sources-from-github)
-  * [Using Git Remotes](#using-git-remotes)
-  * [Build Hugo with Your Changes](#build-hugo-with-your-changes)
-  * [Updating the Hugo Sources](#updating-the-hugo-sources)
+  * [Building Hugo with Your Changes](#building-hugo-with-your-changes)
 
 ## Asking Support Questions
 
@@ -106,7 +103,7 @@ Fixes #1949
 
 ###  Fetching the Sources From GitHub
 
-Since Hugo 0.48, Hugo uses the Go Modules support built into Go 1.11 to build. The easiest is is to clone Hugo in a directory outside of `GOPATH`, as in the following example:
+Since Hugo 0.48, Hugo uses the Go Modules support built into Go 1.11 to build. The easiest is to clone Hugo in a directory outside of `GOPATH`, as in the following example:
 
 ```bash
 mkdir $HOME/src
@@ -191,14 +188,3 @@ mage -l
 HUGO_BUILD_TAGS=extended mage install
 ````
 
-### Updating the Hugo Sources
-
-If you want to stay in sync with the Hugo repository, you can easily pull down
-the source changes, but you'll need to keep the vendored packages up-to-date as
-well.
-
-```bash
-git pull
-mage vendor
-```
-

README.md

@@ -4,7 +4,7 @@ A Fast and Flexible Static Site Generator built with love by [bep](https://githu
 
 [Website](https://gohugo.io) |
 [Forum](https://discourse.gohugo.io) |
-[Developer Chat (no support)](https://gitter.im/gohugoio/hugo) |
+[Developer Chat (no support)](https://gitter.im/spf13/hugo) |
 [Documentation](https://gohugo.io/overview/introduction/) |
 [Installation Guide](https://gohugo.io/overview/installing/) |
 [Contribution Guide](CONTRIBUTING.md) |
@@ -13,7 +13,7 @@ A Fast and Flexible Static Site Generator built with love by [bep](https://githu
 [![GoDoc](https://godoc.org/github.com/gohugoio/hugo?status.svg)](https://godoc.org/github.com/gohugoio/hugo)
 [![Linux and macOS Build Status](https://api.travis-ci.org/gohugoio/hugo.svg?branch=master&label=Linux+and+macOS+build "Linux and macOS Build Status")](https://travis-ci.org/gohugoio/hugo)
 [![Windows Build Status](https://ci.appveyor.com/api/projects/status/a5mr220vsd091kua?svg=true&label=Windows+build "Windows Build Status")](https://ci.appveyor.com/project/bep/hugo/branch/master)
-[![Dev chat at https://gitter.im/gohugoio/hugo](https://img.shields.io/badge/gitter-developer_chat-46bc99.svg)](https://gitter.im/spf13/hugo?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+[![Dev chat at https://gitter.im/spf13/hugo](https://img.shields.io/badge/gitter-developer_chat-46bc99.svg)](https://gitter.im/spf13/hugo?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![Go Report Card](https://goreportcard.com/badge/github.com/gohugoio/hugo)](https://goreportcard.com/report/github.com/gohugoio/hugo)
 
 ## Overview
@@ -61,7 +61,7 @@ Use the [installation instructions in the Hugo documentation](https://gohugo.io/
 
 #### Fetch from GitHub
 
-Since Hugo 0.48, Hugo uses the Go Modules support built into Go 1.11 to build. The easiest is is to clone Hugo in a directory outside of `GOPATH`, as in the following example:
+Since Hugo 0.48, Hugo uses the Go Modules support built into Go 1.11 to build. The easiest is to clone Hugo in a directory outside of `GOPATH`, as in the following example:
 
 ```bash
 mkdir $HOME/src