Fix lints in Dockerfile (CTFd#2097)

* Fix lints in Dockerfile

Author: ColdHeat

.github/workflows/lint.yml

@@ -10,7 +10,7 @@ jobs:
 
     strategy:
       matrix:
-        python-version: ['3.7']
+        python-version: ['3.9']
 
     name: Linting
     steps:

Dockerfile

@@ -25,13 +25,14 @@ RUN for d in CTFd/plugins/*; do \
         fi; \
     done;
 
+# hadolint ignore=DL3059
 RUN adduser \
     --disabled-login \
     -u 1001 \
     --gecos "" \
     --shell /bin/bash \
-    ctfd
-RUN chmod +x /opt/CTFd/docker-entrypoint.sh \
+    ctfd \
+    && chmod +x /opt/CTFd/docker-entrypoint.sh \
     && chown -R 1001:1001 /opt/CTFd /var/log/CTFd /var/uploads
 
 USER 1001