Update build.sh script to use new fabrikate semver semantics

[evanlouie]

As a: operator

I want:

the build.sh script to NOT prefix the the $VERSION_TO_DOWNLOAD link with v

OR

Use the go1.13 installation available on all
ubuntu 16
and
ubuntu 18
hosted vms and update all azure-pipelines.yaml which require fab to include:

variables:
  GOROOT: "/usr/local/go1.13" # Go installation path
  GO111MODULE: "on"

and have just have download_fab() changed to:

function download_fab() {
  go get -v github.com/microsoft/fabrikate # automatically downloads the latest tagged release and installs the fabrikate binary as "fabrikate"
  alias fab=fabrikate # give "fabrikate" a "fab" alias to not break existing pipelines
}

So that: Fabrikate can start publishing proper golang spec'd semver releases
(which require v prefix) and those new releases won't break the build.sh
script

Describe the solution you'd like:

Either of the 2 mentioned above. The latter using go get... is simpler overall
and falls more inline with community semantics of how to do Golang releases.

Acceptance Criteria:

Describe alternatives you've considered:

Additional context:

Does this require updates to documentation?:

[andrebriggs]

@evanlouie is this still an issue?

[evanlouie]

Yes -- not required, but nice to have. Another issue that might want to add to this one is pinning the fabrikate download to a specific semver (i.e 0.x.x) so we can unblock microsoft/fabrikate#296.