Add "curl" to the Docker images for potential use in automations.

docker/Dockerfile

@@ -117,7 +117,8 @@ RUN apk -U add \
         mandoc \
         mosquitto \
         popt \
-        soxr && \
+        soxr \
+        curl && \
     rm -rfv /lib/apk/db/* && \
     rm -rfv /etc/avahi/services/*.service && \
     addgroup shairport-sync && \

docker/classic/Dockerfile

@@ -71,7 +71,8 @@ RUN apk -U add \
         mbedtls \
         mosquitto \
         popt \
-        soxr
+        soxr \
+        curl
 
 # Copy build files.
 COPY --from=builder /shairport-sync/build/install/usr/local/bin/shairport-sync /usr/local/bin/shairport-sync