Remove packages for libreadline from dockerfiles (#54)

Readline has been removed from stdlib since Crystal 0.32.0

Author: straight-shoota

docker/alpine.Dockerfile

@@ -5,7 +5,7 @@ RUN \
     # core dependencies
     gc-dev gcc gmp-dev libatomic_ops libevent-static musl-dev pcre-dev \
     # stdlib dependencies
-    libxml2-dev openssl-dev openssl-libs-static readline-dev tzdata yaml-dev zlib-static \
+    libxml2-dev openssl-dev openssl-libs-static tzdata yaml-dev zlib-static \
     # dev tools
     make git
 

docker/ubuntu.Dockerfile

@@ -21,7 +21,7 @@ FROM runtime as build
 
 RUN \
   apt-get update && \
-  apt-get install -y build-essential llvm-8 libedit-dev libreadline-dev gdb && \
+  apt-get install -y build-essential llvm-8 libedit-dev gdb && \
   apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
 ENV LIBRARY_PATH=/usr/lib/crystal/lib/