Breaking: bump Python from 2.x to 3.x (#15)

As is required for latest `node-gyp`. Some images already had Python
3 installed, now alpine and centos7-devtoolset7 do too, additionally
with the `python` command linked to `python3`. Meaning `python -V`
will print a 3.x version number.

On centos7-devtoolset7, Python 2 remains installed because `yum`
relies on it. It can also be accessed as the `python2` command.

Author: vweevers

README.md

@@ -8,10 +8,10 @@
 
 ## About
 
-All images include `node`, `npm`, `npx` and a preconfigured build toolchain suitable for `node-gyp` and `prebuildify`. For example:
+All images include Node.js LTS, Python 3.x, npm and a preconfigured build toolchain suitable for `node-gyp` and `prebuildify`. For example:
 
 ```
-> docker run --rm -it ghcr.io/prebuild/alpine node -v
+> docker run --rm ghcr.io/prebuild/alpine node -v
 v14.17.4
 ```
 
@@ -25,8 +25,6 @@ FROM ghcr.io/prebuild/alpine:1
 
 Within a major version range, we will not change toolchains, environment variables, working directories, users and more. However, the Node.js version will change without notice. We use Node.js [LTS](https://github.com/nodejs/Release) (at the time of building images) for a light maintenance effort. This is okay because `prebuildify` can target (the headers of) older Node.js versions while itself running on a newer version.
 
-We've yet to align Python versions ([#15](https://github.com/prebuild/docker-images/issues/15)). A next major will use Python 3.
-
 Images that are based on [`dockcross`](https://github.com/dockcross/dockcross) (see below) may inadvertently introduce breaking changes because `dockcross` does not use semantic versions ([dockcross/dockcross#399](https://github.com/dockcross/dockcross/issues/399)) and does not maintain a changelog that would allow us to easily categorize changes and then tag our images accordingly. If this concerns you we recommend pinning to an exact version (`x.x.x`) which we treat as immutable.
 
 ## Images

alpine/Dockerfile

@@ -2,7 +2,9 @@ FROM node:lts-alpine
 
 RUN addgroup -g 2000 travis && \
   adduser -u 2000 -G travis -s /bin/sh -D travis && \
-  apk --no-cache add g++ gcc libgcc libstdc++ linux-headers make python git
+  apk --no-cache add g++ gcc libgcc libstdc++ linux-headers make python3 git && \
+  ln -sf python3 /usr/bin/python && \
+  python --version
 
 USER node
 

centos7-devtoolset7/Dockerfile

@@ -5,8 +5,13 @@ USER 0
 RUN groupadd -g 1000 node && useradd -g 1000 -u 1000 -m node && \
   groupadd -g 2000 travis && useradd -g 2000 -u 2000 -m travis && \
   curl -fsSL https://rpm.nodesource.com/setup_lts.x | bash - && \
-  yum install -y make nodejs && \
-  npm -v
+  yum install -y make nodejs python3 && \
+  sed -i 's/#!\/usr\/bin\/python/#!\/usr\/bin\/python2/' /usr/bin/yum && \
+  ln -sf python3 /usr/bin/python && \
+  yum clean all && \
+  rm -rf /var/cache/yum && \
+  npm -v && \
+  python --version
 
 USER node