Install git command for alpine versions.

[miry]

go-wrapper depends on git command.

This exception I got when used golang:1.9-alpine

Status: Downloaded newer image for golang:1.9-alpine
 ---> bbab7aea1231
Step 2/8 : WORKDIR /go/src/app
Removing intermediate container 53b495380373
 ---> f447f8a09abe
Step 3/8 : COPY . .
 ---> 1d5935656e53
Step 4/8 : RUN go-wrapper download  && go-wrapper install
 ---> Running in e953b094261b
+ exec go get -v -d
github.com/PagerDuty/go-pagerduty (download)
go: missing Git command. See https://golang.org/s/gogetcmd
package github.com/PagerDuty/go-pagerduty: exec: "git": executable file not found in $PATH
github.com/nlopes/slack (download)
go: missing Git command. See https://golang.org/s/gogetcmd
package github.com/nlopes/slack: exec: "git": executable file not found in $PATH
The command '/bin/sh -c go-wrapper download  && go-wrapper install' returned a non-zero code: 1

[tianon]

Duplicate of #157 (see also #119).

In short, git is not included in the Alpine variants on purpose (as described in #119 and the image description).

[miry]

@tianon thanks. I searched and did not find those. Good to know. Commented the original issue.

I think all golang dockers should be consistent and have pretty the same basic commands.