* docs: Add note to install Testify
The Hugo Contributor Guide (Development) instructs users to run "go test ./..." and ensure it passes before moving on. However Hugo requires the Testify package for testing, and running the go test command without Testify results in 'cannot find package' errors and failing tests. It's hard to understand what to do next for users not familiar with Go dependencies. This commit adds a note to the contributor guide instructing users to get Testify if they don't already have it installed. Running the 'go get' command added here results in passing tests in the next step of the contributor guide.
* Fix typo https:// in go get command
See https://www.netlify.com/blog/2017/07/18/http/2-server-push-on-netlify/
```
▶ nghttp -ans https://deploy-preview-83--gohugoio.netlify.com/
***** Statistics *****
Request timing:
responseEnd: the time when last byte of response was received
relative to connectEnd
requestStart: the time just before first byte of request was sent
relative to connectEnd. If '*' is shown, this was
pushed by server.
process: responseEnd - requestStart
code: HTTP status code
size: number of bytes received as response body without
inflation.
URI: request URI
see http://www.w3.org/TR/resource-timing/#processing-model
sorted by 'complete'
id responseEnd requestStart process code size request path
13 +199.52ms +1.22ms 198.30ms 200 42K /
4 +404.60ms * +69.97ms 334.62ms 200 102K /dist/main.css
2 +484.93ms * +69.63ms 415.30ms 200 131K /dist/app.bundle.js
```
Compare that to the live site:
```
▶ nghttp -ans https://gohugo.io/
***** Statistics *****
Request timing:
responseEnd: the time when last byte of response was received
relative to connectEnd
requestStart: the time just before first byte of request was sent
relative to connectEnd. If '*' is shown, this was
pushed by server.
process: responseEnd - requestStart
code: HTTP status code
size: number of bytes received as response body without
inflation.
URI: request URI
see http://www.w3.org/TR/resource-timing/#processing-model
sorted by 'complete'
id responseEnd requestStart process code size request path
13 +596.97ms +2.54ms 594.43ms 200 42K /
15 +606.87ms +403.50ms 203.37ms 200 15K /files/muli-latin-200.woff2
2`1 +790.39ms +403.51ms 386.88ms 200 20K /dist/main.css
23 +1.14s +596.00ms 544.48ms 200 42K /dist/app.bundle.js
19 +1.14s +403.50ms 737.99ms 200 15K /files/muli-latin-800.woff2
17 +1.14s +403.50ms 738.01ms 200 15K /files/muli-latin-400.woff2
```
