Dockerfile: fixed ENV var syntax

Dockerfile

@@ -27,11 +27,11 @@ RUN npm run build
 #-----------------------------------------
 # STAGE 3: Run the Next.js server
 #-----------------------------------------
-FROM base as production
+FROM base AS production
 
 WORKDIR /app
 
-ENV NODE_ENV production
+ENV NODE_ENV=production
 
 RUN addgroup --system --gid 1001 nodejs
 RUN adduser --system --uid 1001 nextjs
@@ -54,7 +54,7 @@ USER nextjs
 
 EXPOSE 3000
 
-ENV PORT 3000
+ENV PORT=3000
 
 # server.js is created by next build from the standalone output
 # https://nextjs.org/docs/pages/api-reference/next-config-js/output