Issue #15: Added JAVA_OPTS env variable to set UTF-8 encoding

Author: Robert Winkler

Dockerfile

@@ -5,4 +5,6 @@ WORKDIR /usr/bin/swagger2markup
 
 RUN apk update && apk add ca-certificates wget && update-ca-certificates && wget https://jcenter.bintray.com/io/github/swagger2markup/swagger2markup-cli/1.3.1/swagger2markup-cli-1.3.1.jar
 
+ENV JAVA_OPTS="-Dfile.encoding=UTF-8 -Dsun.jnu.encoding=UTF-8"
+
 ENTRYPOINT ["java","-jar","/usr/bin/swagger2markup/swagger2markup-cli-1.3.1.jar"]