Prepare 4.0.1 release

[wing328]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\. If contributing template-only or documentation-only changes which will change sample output, be sure to build the project first.
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Description of the PR

(details of the change, additional tests that have been done, reference to the issue for tracking, etc)

[jmini]

As discussed on Gitter, this PR should update this line to 4.0.1:

openapi-generator/modules/openapi-generator-gradle-plugin/gradle.properties

Line 1 in 39648ee

openApiGeneratorVersion=4.0.1-SNAPSHOT

in modules/openapi-generator-gradle-plugin/gradle.properties

@jimschubert indicated that the script is only working with version in XML tags:

openapi-generator/bin/utils/release_version_update.sh

Lines 36 to 60 in 7ecc991

	declare -a files=("modules/openapi-generator-cli/pom.xml"
	"modules/openapi-generator-gradle-plugin/gradle.properties"
	"modules/openapi-generator-gradle-plugin/pom.xml"
	"modules/openapi-generator-core/pom.xml"
	"modules/openapi-generator-maven-plugin/pom.xml"
	"modules/openapi-generator-online/pom.xml"
	"modules/openapi-generator/pom.xml"
	"samples/meta-codegen/lib/pom.xml"
	"pom.xml")
	sedi () {
	# Cross-platform version of sed -i that works both on Mac and Linux
	sed --version >/dev/null 2>&1 && sed -i -e "$@" || sed -i "" "$@"
	}
	for filename in "${files[@]}"; do
	# e.g. sed -i '' "s/3.0.1-SNAPSHOT/3.0.1/g" CI/pom.xml.bash
	#echo "Running command: sed -i '' "s/$FROM/$TO/g" $filename"
	if sedi "s/>$FROM</>$TO</g" $filename; then
	echo "Updated $filename successfully!"
	else
	echo "ERROR: Failed to update $filename with the following command"
	echo "sed -i '' \"s/$FROM/$TO/g\" $filename"
	fi
	done

This must be fixed.

[jimschubert]

I fixed the mentioned script in commit a553408 in #3047