Improve docker build process

docker/Dockerfile

@@ -1,4 +1,6 @@
-FROM php:7.2-cli
+ARG PHP_BASE_IMAGE
+
+FROM ${PHP_BASE_IMAGE}
 
 # Project folder
 RUN mkdir -p /srv/app
@@ -10,11 +12,11 @@ RUN apt-get update \
     && rm -rf /var/lib/apt/lists/*
 
 # get composer and required tools
-RUN curl -sLO https://getcomposer.org/download/1.6.3/composer.phar \
+RUN curl -sLO https://getcomposer.org/download/1.6.4/composer.phar \
     && mv composer.phar /usr/local/bin/composer \
     && chmod +x /usr/local/bin/composer
 
 # Deployer
-RUN curl -sLO https://deployer.org/releases/v6.0.3/deployer.phar \
+RUN curl -sLO https://deployer.org/releases/v6.2.0/deployer.phar \
     && mv deployer.phar /usr/local/bin/dep \
     && chmod +x /usr/local/bin/dep