bump dockerfiles to go 1.16

docker/Dockerfile

@@ -2,7 +2,7 @@
 
 # Base Go environment
 # -------------------
-FROM golang:1.15-alpine as base
+FROM golang:1.16-alpine as base
 WORKDIR /porter
 
 RUN apk update && apk add --no-cache gcc musl-dev git

docker/cli.Dockerfile

@@ -2,7 +2,7 @@
 
 # Base Go environment
 # -------------------
-FROM golang:1.15 as base
+FROM golang:1.16 as base
 WORKDIR /porter
 
 RUN apt-get update && apt-get install -y gcc musl-dev git make

docker/dev.Dockerfile

@@ -1,6 +1,6 @@
 # Development environment
 # -----------------------
-FROM golang:1.15-alpine
+FROM golang:1.16-alpine
 WORKDIR /porter
 
 RUN apk update && apk add --no-cache gcc musl-dev git

ee/docker/ee.Dockerfile

@@ -2,7 +2,7 @@
 
 # Base Go environment
 # -------------------
-FROM golang:1.15-alpine as base
+FROM golang:1.16-alpine as base
 WORKDIR /porter
 
 RUN apk update && apk add --no-cache gcc musl-dev git