Use newer centos image

[killuazhu]

Use newer base image and update packages to reduce vulnerabilities in the image.

When you use trivy to scan the latest image, it contains many fixable vulnerabilities, most of them comes from centos:7 base image

sudo trivy image --ignore-unfixed lightbend/kafka-lag-exporter:0.6.4
2020-10-08T22:44:51.188Z        INFO    Detecting RHEL/CentOS vulnerabilities...

lightbend/kafka-lag-exporter:0.6.4 (centos 7.8.2003)
====================================================
Total: 112 (UNKNOWN: 0, LOW: 23, MEDIUM: 81, HIGH: 8, CRITICAL: 0)

......did not include the full output.....

[lightbend-cla-validator]

Hi @killuazhu,

Thank you for your contribution! We really value the time you've taken to put this together.

Before we proceed with reviewing this pull request, please sign the Lightbend Contributors License Agreement:

https://www.lightbend.com/contribute/cla

[killuazhu]

@seglo the build is passing. Could you please review and merge? Thanks.

[seglo]

Thanks @killuazhu

[killuazhu]

@seglo thanks for merging the change. Could you please also make a release? We'd like to consume the updated image on docker hub.

Thanks in advance.

[seglo]

Sure. Here it is:

https://github.com/lightbend/kafka-lag-exporter/releases/tag/v0.6.5

[killuazhu]

Awesome! Thanks @seglo