Upgrade to jsonnet version 0.12.1

This is to avoid running into this bug: google/jsonnet#531

Author: csmarchbanks

.circleci/Dockerfile

@@ -4,7 +4,7 @@ FROM alpine:3.7
 RUN apk --no-cache add alpine-sdk git openssl-dev
 
 RUN git clone https://github.com/google/jsonnet && \
-    git  -C jsonnet checkout v0.10.0 && \
+    git  -C jsonnet checkout v0.12.1 && \
     make -C jsonnet LDFLAGS=-static
 
 FROM circleci/golang:1.10.3-stretch

.circleci/config.yml

@@ -2,7 +2,7 @@ version: 2
 jobs:
   build:
     docker:
-      - image: tomwilkie/kubernetes-mixin-build:dont-commit-binary
+      - image: csmarchbanks/kubernetes-mixin-build:jsonnet-0.12.1
 
     working_directory: /go/src/github.com/kubernetes-monitoring/kubernetes-mixin
     steps: