Fixed typo in dockerfile with apt-purge instead of apt purge

Signed-off-by: Louis Vallat <louis@louis-vallat.xyz>

Dockerfile

@@ -8,5 +8,5 @@ RUN apt-get update \
     && service apache2 restart \
     && mv "$PHP_INI_DIR/php.ini-production" "$PHP_INI_DIR/php.ini" \
     && docker-php-ext-install -j$(nproc) opcache \
-    && apt-purge -y wget $(apt-mark showauto) \
+    && apt purge -y wget $(apt-mark showauto) \
     && rm -rf /var/lib/apt/lists/*