fix UTF-8 output in Dockerfile

Dockerfile

@@ -1,6 +1,6 @@
 FROM ubuntu:rolling
 RUN apt-get update && apt-get -y upgrade
-RUN apt-get install -y curl libgmp-dev libbz2-dev libreadline-dev software-properties-common
+RUN apt-get install -y curl libgmp-dev libbz2-dev libreadline-dev software-properties-common locales-all locales
 RUN add-apt-repository -y ppa:ethereum/ethereum
 RUN apt-get update
 RUN apt-get install -y solc
@@ -8,5 +8,10 @@ RUN curl -sSL https://get.haskellstack.org/ | sh
 COPY . /echidna/
 WORKDIR /echidna
 RUN stack upgrade && stack setup && stack install
-ENV PATH=$PATH:$HOME/.local/bin
+ENV PATH=$PATH:/root/.local/bin
+RUN update-locale LANG=en_US.UTF-8
+RUN locale-gen en_US.UTF-8  
+ENV LANG en_US.UTF-8  
+ENV LANGUAGE en_US:en  
+ENV LC_ALL en_US.UTF-8
 CMD ["echidna-test", "solidity/cli.sol"]