fix: Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-DEBIAN9-GIT-340821
- https://snyk.io/vuln/SNYK-DEBIAN9-GIT-340908
- https://snyk.io/vuln/SNYK-DEBIAN9-PROCPS-309314
- https://snyk.io/vuln/SNYK-DEBIAN9-SUBVERSION-456173
- https://snyk.io/vuln/SNYK-DEBIAN9-WGET-342192

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.10.1
+FROM golang:1.15
 
 # Install pact ruby standalone binaries
 RUN curl -LO https://github.com/pact-foundation/pact-ruby-standalone/releases/download/v1.37.0/pact-1.37.0-linux-x86_64.tar.gz; \