Bump vaadin-bom from 8.4.1 to 8.12.3 in /vaadin8#28

dependabot[bot] wants to merge 1 commit intomastercherkavi/java-web:masterfrom

dependabot/maven/vaadin8/com.vaadin-vaadin-bom-8.12.3cherkavi/java-web:dependabot/maven/vaadin8/com.vaadin-vaadin-bom-8.12.3Copy head branch name to clipboard