Update Dockerfile (#20845)

Update base image, dependencies, add ENTRYPOINT, and don't ADD source to reduce image size

Dockerfile

@@ -1,20 +1,31 @@
-# VERSION:        0.1
-# DESCRIPTION:    Image to build Atom and create a .rpm file
+# VERSION:        0.2
+# DESCRIPTION:    Image to build Atom
 
-# Base docker image
-FROM nodesource/fedora21:4.2.6
+FROM ubuntu:20.04
 
 # Install dependencies
-RUN yum install -y \
-    make \
-    gcc \
-    gcc-c++ \
-    glibc-devel \
-    git-core \
-    libsecret-devel \
-    rpmdevtools
+RUN apt-get update && \
+    DEBIAN_FRONTEND="noninteractive" \
+    apt-get install -y \
+        build-essential \
+        git \
+        libsecret-1-dev \
+        fakeroot \
+        rpm \
+        libx11-dev \
+        libxkbfile-dev \
+        libgdk-pixbuf2.0-dev \
+        libgtk-3-dev \
+        libxss-dev \
+        libasound2-dev \
+        npm && \
+    rm -rf /var/lib/apt/lists/*
 
+# Update npm and dependencies
 RUN npm install -g npm --loglevel error
 
-ADD . /atom
-WORKDIR /atom
+# Use python2 by default
+RUN npm config set python /usr/bin/python2 -g
+
+ENTRYPOINT ["/usr/bin/env", "sh", "-c"]
+CMD ["bash"]