Dockerfile: User && instead of ;

We don't want to continue if any of the commands fails.
&& only executes the next command on exitocde 0.

Dockerfile

@@ -6,10 +6,10 @@ RUN apt-get update && apt-get install -y \
         libpng12-dev \
         wget \
         zip \
-        unzip; \
+        unzip && \
     # We install and enable php-gd
-    docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/; \
-    docker-php-ext-install -j$(nproc) gd; \
+    docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/ &&\
+    docker-php-ext-install -j$(nproc) gd && \
 
     # We enable Apache's mod_rewrite
     a2enmod rewrite