fix syntex error (#2317)

* fix syntex error cause by #2309

php-fpm/Dockerfile

@@ -364,10 +364,10 @@ ARG INSTALL_MEMCACHED=false
 RUN if [ ${INSTALL_MEMCACHED} = true ]; then \
     # Install the php memcached extension
     if [ $(php -r "echo PHP_MAJOR_VERSION;") = "5" ]; then \
-      pecl install memcached-2.2.0
+      pecl install memcached-2.2.0; \
     else \
-      pecl install memcached-3.1.3
-    fi
+      pecl install memcached-3.1.3; \
+    fi \
     && docker-php-ext-enable memcached \
 ;fi