Update Dockerfiles to not save the apk cache

When installing the Mosquitto package from Alpine Linux, we don't need
to save the latest package index to the cache. We are specifically requesting
the latest package index each time we install Mosquitto and not using the local
cache at all (--no-cache).

Signed-off-by: David Audet <david.audet@ca.com>

docker/1.4.4/Dockerfile

@@ -3,7 +3,7 @@ MAINTAINER David Audet <david.audet@ca.com>
 
 LABEL Description="Eclipse Mosquitto MQTT Broker"
 
-RUN apk --no-cache --update add mosquitto=1.4.4-r0 && \
+RUN apk --no-cache add mosquitto=1.4.4-r0 && \
     mkdir -p /mosquitto/config /mosquitto/data /mosquitto/log && \
     cp /etc/mosquitto/mosquitto.conf /mosquitto/config && \
     chown -R mosquitto:mosquitto /mosquitto

docker/1.4.8/Dockerfile

@@ -3,7 +3,7 @@ MAINTAINER David Audet <david.audet@ca.com>
 
 LABEL Description="Eclipse Mosquitto MQTT Broker"
 
-RUN apk --no-cache --update add mosquitto=1.4.8-r2 && \
+RUN apk --no-cache add mosquitto=1.4.8-r2 && \
     mkdir -p /mosquitto/config /mosquitto/data /mosquitto/log && \
     cp /etc/mosquitto/mosquitto.conf /mosquitto/config && \
     chown -R mosquitto:mosquitto /mosquitto