Refactoring: introduce local, return early

- use #reject
  - add basic spec around it

spec/unit/generator/generator_processor_spec.rb

@@ -0,0 +1,16 @@
+module GitHubChangelogGenerator
+  describe Generator do
+    context "#exclude_issues_by_labels" do
+      let(:label) {  double("the-bad-label", name: "BAD") }
+      let(:issue) { double("the-issue-to-be-excluded", labels: [label]) }
+      let(:issues) { [issue] }
+      subject(:generator) { described_class.new(exclude_labels: %w(BAD BOO))}
+
+      it "removes issues with labels in the exclude_label list" do
+        result = generator.exclude_issues_by_labels(issues)
+
+        expect(result).to be_empty
+      end
+    end
+  end
+end