Bump golang from 1.15.3-alpine3.12 to 1.15.6-alpine3.12 (#125)

Bumps golang from 1.15.3-alpine3.12 to 1.15.6-alpine3.12.

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Dockerfile

@@ -1,7 +1,7 @@
 ############################
 # Build api
 ############################
-FROM golang:1.15.3-alpine3.12 AS apibuilder
+FROM golang:1.15.6-alpine3.12 AS apibuilder
 RUN apk update && apk add --no-cache git dep
 COPY api $GOPATH/src/github.com/alexbrazier/go-url/api
 WORKDIR $GOPATH/src/github.com/alexbrazier/go-url/api