Lock Redis verson for PHP 7.1

php-unit-test/7.1/Dockerfile

@@ -14,7 +14,7 @@ LABEL org.label-schema.build-date=$BUILD_DATE \
 
 RUN apk add --no-cache bash nodejs nodejs-npm libmcrypt-dev $PHPIZE_DEPS \
     && pecl channel-update pecl.php.net \
-    && pecl install xdebug-2.9.8 redis \
+    && pecl install xdebug-2.9.8 redis-5.3.7 \
     && docker-php-ext-enable xdebug redis \
     && docker-php-ext-install mcrypt \
     && apk del --no-cache $PHPIZE_DEPS