Install grep to avoid issues in pihole -w/b with the default busybox grep

Signed-off-by: Adam Warner <me@adamwarner.co.uk>

src/Dockerfile

@@ -21,6 +21,8 @@ RUN apk add --no-cache \
     coreutils \
     curl \
     git \
+    # Install grep to avoid issues in pihole -w/b with the default busybox grep
+    grep \
     iproute2-ss \
     jq \
     libcap \