chore: run apt-get update before running other commands (#41)

This will run `sudo apt-get update` before running any other commands on the Gitpod prebuild image (`.gitpod.dockerfile`).

Author: Panquesito7

.gitpod.dockerfile

@@ -1,6 +1,6 @@
 FROM gitpod/workspace-base
 
-RUN curl https://nim-lang.org/choosenim/init.sh -sSf -o install_nim.sh \
+RUN sudo apt-get update && curl https://nim-lang.org/choosenim/init.sh -sSf -o install_nim.sh \
     && chmod +x ./install_nim.sh \
     && ./install_nim.sh -y \
     && rm install_nim.sh \