update readme file (php section)

workspace/Dockerfile

@@ -6,8 +6,9 @@ RUN DEBIAN_FRONTEND=noninteractive
 RUN locale-gen en_US.UTF-8
 
 ENV LANGUAGE=en_US.UTF-8
-ENV LANG=en_US.UTF-8
 ENV LC_ALL=en_US.UTF-8
+ENV LC_CTYPE=UTF-8
+ENV LANG=en_US.UTF-8
 ENV TERM xterm
 
 # Install "software-properties-common" (for add-apt-repository) and add the "PHP 7" ppa