Dockerfiles: Replace deprecated "maintainer" label

Also, do the `dnf install` in one step, not in three.

k8s/Dockerfile-nginx

@@ -16,13 +16,19 @@
 #
 FROM fedora AS sslip.io-nginx
 
-LABEL maintainer="brian.cunnie@gmail.com"
+LABEL org.opencontainers.image.authors="Brian Cunnie <brian.cunnie@gmail.com>"
 
-RUN dnf install -y iproute bind-utils neovim
+RUN dnf install -y \
+    bind-utils \
+    iproute \
+    less \
+    lsof \
+    neovim \
+    net-tools \
+    nginx \
+    nmap-ncat \
+    procps-ng \
 
-RUN dnf install -y procps-ng nmap-ncat net-tools lsof less
-
-RUN dnf install -y nginx
 
 RUN mv /usr/share/nginx/html /usr/share/nginx/html-orig
 

k8s/Dockerfile-ntp

@@ -6,7 +6,7 @@
 # Much was from here: <https://goglides.io/manage-ntp-using-kubernetes/90/>
 
 FROM alpine:3.11.3 AS sslip.io-ntp
-LABEL maintainer="brian.cunnie@gmail.com"
+LABEL org.opencontainers.image.authors="Brian Cunnie <brian.cunnie@gmail.com>"
 RUN apk update
 RUN apk add openntpd
 RUN mkdir -m 1777 /var/empty/tmp

k8s/Dockerfile-sslip.io-dns-server

@@ -21,7 +21,7 @@
 #
 FROM alpine AS sslip.io
 
-LABEL maintainer="brian.cunnie@gmail.com"
+LABEL org.opencontainers.image.authors="Brian Cunnie <brian.cunnie@gmail.com>"
 
 RUN apk update && apk add bind-tools
 

k8s/Dockerfile-wildcard-dns-http-server

@@ -39,7 +39,7 @@
 
 FROM alpine AS sslip.io
 
-LABEL maintainer="brian.cunnie@gmail.com"
+LABEL org.opencontainers.image.authors="Brian Cunnie <brian.cunnie@gmail.com>"
 
 COPY wildcard-dns-http-server /usr/sbin/wildcard-dns-http-server