INTERNAL: Fix deprecated items, centos:7 to rockylinux:8 and `ENV…

… key value` to `ENV key=value`, in Dockerfile.

Dockerfile

@@ -1,4 +1,4 @@
-FROM centos:7 AS builder
+FROM rockylinux:8 AS builder
 RUN yum update -y
 RUN yum install -y make libtool which git
 # Copy all files from the repository not included in .dockerignore to /src in the image.
@@ -9,9 +9,9 @@ RUN ./config/autorun.sh
 RUN ./configure --prefix=/arcus --enable-zk-integration
 RUN make && make install
 
-FROM centos:7 AS base
+FROM rockylinux:8 AS base
 COPY --from=builder /arcus /arcus
-ENV PATH ${PATH}:/arcus/bin
+ENV PATH=${PATH}:/arcus/bin
 
 EXPOSE 11211/tcp
 
@@ -27,8 +27,8 @@ FROM base
 RUN yum update -y
 RUN yum install -y bind-utils nc
 RUN yum clean all -y
-ENV MEMCACHED_DIR /arcus-memcached
-ENV PATH ${PATH}:${MEMCACHED_DIR}
-ENV ARCUS_USER root
+ENV MEMCACHED_DIR=/arcus-memcached
+ENV PATH=${PATH}:${MEMCACHED_DIR}
+ENV ARCUS_USER=root
 WORKDIR ${MEMCACHED_DIR}
 RUN ln -s /arcus/lib ${MEMCACHED_DIR}/.libs