Update Dockerfile

Dockerfile

@@ -4,9 +4,8 @@ MAINTAINER Florian Thöni <florian.thoni@floth.fr>
 ENV DEBIAN_FRONTEND noninteractive
 
 RUN apt-get update; \
-   apt-get install -y build-essential && \
+   apt-get install -y build-essential curl && \
    apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
 RUN curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.6/install.sh | bash
-RUN source "~/.nvm/nvm.sh"
-RUN nvm install 6
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+RUN . "~/.nvm/nvm.sh" && nvm install 6
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