fix issues in Dockerfile

Dockerfile

@@ -3,9 +3,10 @@ FROM ubuntu:14.04
 # Install packages for building ruby
 RUN apt-get install -y software-properties-common
 RUN apt-add-repository -y ppa:brightbox/ruby-ng
-RUN apt-get update
+RUN apt-get update -y
+RUN apt-get upgrade -y
 RUN apt-get install -y --force-yes build-essential curl wget git
-RUN apt-get install -y --force-yes zlib1g-dev libssl-dev libreadline-dev libyaml-dev libxml2-dev libxslt-dev ruby2.1
+RUN apt-get install -y --force-yes zlib1g-dev libssl-dev libreadline-dev libyaml-dev libxml2-dev libxslt-dev ruby2.1 ruby2.1-dev
 RUN apt-get clean
 RUN gem install bundler foreman
 RUN mkdir -p /var/app
@@ -18,7 +19,7 @@ ENV RACK_ENV production
 # Define working directory.
 WORKDIR /var/app
 
-RUN git clone git@github.com:mcansky/sinatra_hello.git /var/app
+RUN git clone https://github.com/mcansky/sinatra_hello.git /var/app
 RUN cd /var/app; bundle install
 
 EXPOSE 3000