Added ability to select genesis version as the tag

Author: dennisjbell

Dockerfile

@@ -21,7 +21,9 @@ RUN apt-get update \
  && curl -Lo /usr/bin/bosh https://github.com/cloudfoundry/bosh-cli/releases/download/v6.2.1/bosh-cli-6.2.1-linux-amd64 \
      && chmod 0755 /usr/bin/bosh
 
-RUN curl -Lo /usr/bin/genesis https://github.com/genesis-community/genesis/releases/download/v2.7.4/genesis \
+ARG GENESIS_VERSION
+
+RUN curl -Lo /usr/bin/genesis https://github.com/genesis-community/genesis/releases/download/v$GENESIS_VERSION/genesis \
      && chmod 0755 /usr/bin/genesis
 
 RUN genesis -v

Makefile

@@ -2,7 +2,7 @@ IMAGE := starkandwayne/genesis
 TAG   ?= 2.7.1
 
 build:
-	docker build -t $(IMAGE):dev .
+	docker build -t $(IMAGE):dev --build-arg GENESIS_VERSION=$(TAG) .
 	docker run $(IMAGE):dev genesis -v
 release: build
 	docker tag $(IMAGE):dev $(IMAGE):latest