Fix the PHP Docker image

docker/php/Dockerfile

@@ -1,13 +1,12 @@
 FROM php:7.3-fpm
 
-RUN docker-php-ext-install \
-    mysqli \
-    pdo \
-    openssl \
-    mbstring \
-    tokenizer \
-    curl \
-    json \
-    gmp
+RUN apt-get update
+RUN apt-get install -y libgmp-dev
 
 RUN ln -sf /dev/stderr /var/log/fpm-error.log
+
+RUN docker-php-ext-install \
+  mysqli \
+  pdo \
+  pdo_mysql \
+  gmp