[doc] Fix github issue templates

The labels were wrong, maybe now they are assigned
automatically...

.github/ISSUE_TEMPLATE/bug_report.md

@@ -2,7 +2,7 @@
 name: Bug report
 about: Create a report to help us improve
 title: ''
-labels: bug
+labels: 'a:bug'
 assignees: ''
 
 ---

.github/ISSUE_TEMPLATE/feature_request.md

@@ -2,7 +2,7 @@
 name: Feature request
 about: Suggest an idea for this project
 title: ''
-labels: enhancement
+labels: 'an:enhancement'
 assignees: ''
 
 ---

.github/ISSUE_TEMPLATE/new_rule.md

@@ -2,7 +2,7 @@
 name: New Rule
 about: You have an idea for a new rule? Great!
 title: ''
-labels: new-rule
+labels: 'a:new-rule'
 assignees: ''
 
 ---

.github/ISSUE_TEMPLATE/question.md

@@ -2,7 +2,7 @@
 name: Question
 about: Feel free to ask any question about PMD and its usage
 title: ''
-labels: question
+labels: 'a:question'
 assignees: ''
 
 ---

.github/ISSUE_TEMPLATE/rule_violation.md

@@ -2,7 +2,7 @@
 name: Rule violation
 about: Let us know about a false positive/false negative
 title: ''
-labels: bug
+labels: 'a:bug'
 assignees: ''
 
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