Bump version from 3.9.0 to 3.9.1

[ademidoff]

https://jira.percona.com/browse/PMM-7

[JNKPercona]

Server docker: perconalab/pmm-server-fb:PR-4502-2879c5e
Client docker: perconalab/pmm-client-fb:PR-4502-2879c5e
Watchtower docker: perconalab/pmm-watchtower-fb:PR-4502-2879c5e
Client tarball: https://s3.us-east-2.amazonaws.com/pmm-build-cache/PR-BUILDS/pmm-client/pmm-client-PR-4502-2879c5e.tar.gz
Staging instance: https://pmm.cd.percona.com/job/pmm3-aws-staging-start/parambuild/?DOCKER_VERSION=perconalab/pmm-server-fb:PR-4502-2879c5e&CLIENT_VERSION=https://s3.us-east-2.amazonaws.com/pmm-build-cache/PR-BUILDS/pmm-client/pmm-client-PR-4502-2879c5e.tar.gz

[JNKPercona]

API tests have succeded: https://pmm.cd.percona.com/job/pmm3-api-tests/6908/

[JNKPercona]

Server docker: perconalab/pmm-server-fb:PR-4502-30cf6f1
Client docker: perconalab/pmm-client-fb:PR-4502-30cf6f1
Watchtower docker: perconalab/pmm-watchtower-fb:PR-4502-30cf6f1
Client tarball: https://s3.us-east-2.amazonaws.com/pmm-build-cache/PR-BUILDS/pmm-client/pmm-client-PR-4502-30cf6f1.tar.gz
Staging instance: https://pmm.cd.percona.com/job/pmm3-aws-staging-start/parambuild/?DOCKER_VERSION=perconalab/pmm-server-fb:PR-4502-30cf6f1&CLIENT_VERSION=https://s3.us-east-2.amazonaws.com/pmm-build-cache/PR-BUILDS/pmm-client/pmm-client-PR-4502-30cf6f1.tar.gz

[JNKPercona]

API tests have succeded: https://pmm.cd.percona.com/job/pmm3-api-tests/6909/

[JNKPercona]

Server docker: perconalab/pmm-server-fb:PR-4502-7912686
Client docker: perconalab/pmm-client-fb:PR-4502-7912686
Watchtower docker: perconalab/pmm-watchtower-fb:PR-4502-7912686
Client tarball: https://s3.us-east-2.amazonaws.com/pmm-build-cache/PR-BUILDS/pmm-client/pmm-client-PR-4502-7912686.tar.gz
Staging instance: https://pmm.cd.percona.com/job/pmm3-aws-staging-start/parambuild/?DOCKER_VERSION=perconalab/pmm-server-fb:PR-4502-7912686&CLIENT_VERSION=https://s3.us-east-2.amazonaws.com/pmm-build-cache/PR-BUILDS/pmm-client/pmm-client-PR-4502-7912686.tar.gz

[JNKPercona]

API tests have succeded: https://pmm.cd.percona.com/job/pmm3-api-tests/6913/

[JNKPercona]

Server docker: perconalab/pmm-server-fb:PR-4502-e118c56
Client docker: perconalab/pmm-client-fb:PR-4502-e118c56
Watchtower docker: perconalab/pmm-watchtower-fb:PR-4502-e118c56
Client tarball: https://s3.us-east-2.amazonaws.com/pmm-build-cache/PR-BUILDS/pmm-client/pmm-client-PR-4502-e118c56.tar.gz
Staging instance: https://pmm.cd.percona.com/job/pmm3-aws-staging-start/parambuild/?DOCKER_VERSION=perconalab/pmm-server-fb:PR-4502-e118c56&CLIENT_VERSION=https://s3.us-east-2.amazonaws.com/pmm-build-cache/PR-BUILDS/pmm-client/pmm-client-PR-4502-e118c56.tar.gz

[JNKPercona]

API tests have succeded: https://pmm.cd.percona.com/job/pmm3-api-tests/6924/