fix build - add / at the end of directory

Author: sopitz

Dockerfile

@@ -4,7 +4,7 @@ RUN apt-get update && apt-get install -y git && apt-get clean && rm -rf /var/lib
 RUN cd / && git clone https://github.com/letsencrypt/letsencrypt
 
 COPY etc /etc
-COPY ssl.tmpl /app
+COPY ssl.tmpl /app/
 COPY createSSL.sh /
 RUN chmod +x /createSSL.sh
 COPY Procfile /app/Procfile