feat(semantic-release): use `sed` to update python version

The `semantic-release-pypi` only works with `setup.py` / `setup.cfg`.

BREAKING CHANGE: use `@semantic-release/exec` instead of `semantic-release-pypi`

* .releaserc.js: define an example using `@semantic-release/exec` to
  execute a `sed` command.

.releaserc.js

@@ -146,18 +146,19 @@ if (
 // );
 // gitAssets.push('app/package*.json');
 
-// // We need to update setup.py
+// // Python: update the version string in the module file
+// // Use sed to change the version string in a file
+// const sedVersionFile = './src/version.py';
+// var sedVersionCmd = "sed -i -e 's,^\\(.*__version__\\).*,\\1 = \"${nextRelease.version}\",' ";
 // config.plugins.push(
 //   [
-//     'semantic-release-pypi',
+//     '@semantic-release/exec',
 //     {
-//       setupPy: 'setup.py',
-//       pypiPublish: false,
+//       prepareCmd: sedVersionCmd.concat(sedVersionFile),
 //     },
 //   ]
 // );
-// gitAssets.push('setup.cfg');
-
+// gitAssets.push(sedVersionFile);
 
 // // Update Helm chart version
 // config.plugins.push(