test v2.x against node 12, 14, 16 (#3390)

Author: tlhunter

.gitlab/benchmarks.yml

@@ -70,6 +70,12 @@ benchmark:
   extends: .benchmarks
   parallel:
     matrix:
+      - MAJOR_VERSION: 12
+        GROUP: 1
+      - MAJOR_VERSION: 12
+        GROUP: 2
+      - MAJOR_VERSION: 12
+        GROUP: 3
       - MAJOR_VERSION: 14
         GROUP: 1
       - MAJOR_VERSION: 14
@@ -82,11 +88,5 @@ benchmark:
         GROUP: 2
       - MAJOR_VERSION: 16
         GROUP: 3
-      - MAJOR_VERSION: 18
-        GROUP: 1
-      - MAJOR_VERSION: 18
-        GROUP: 2
-      - MAJOR_VERSION: 18
-        GROUP: 3
   variables:
     SPLITS: 3