chore(travis): add 4.2 testing to travis

Author: daprahamian

.travis.yml

@@ -53,11 +53,21 @@ jobs:
       env:
         - MONGODB_VERSION=4.0.x
         - MONGODB_ENVIRONMENT=replicaset
+    - stage: replicaset
+      node_js: 4
+      env:
+        - MONGODB_VERSION=4.2.x
+        - MONGODB_ENVIRONMENT=replicaset
     - stage: sharded
       node_js: 4
       env:
         - MONGODB_VERSION=4.0.x
         - MONGODB_ENVIRONMENT=sharded
+    - stage: sharded
+      node_js: 4
+      env:
+        - MONGODB_VERSION=4.2.x
+        - MONGODB_ENVIRONMENT=sharded
 
     # basic smoke test of the unified topology
     - stage: unified
@@ -77,6 +87,18 @@ jobs:
         - MONGODB_VERSION=4.0.x
         - MONGODB_UNIFIED_TOPOLOGY=1
         - MONGODB_ENVIRONMENT=sharded
+    - stage: unified
+      node_js: 4
+      env:
+        - MONGODB_VERSION=4.2.x
+        - MONGODB_UNIFIED_TOPOLOGY=1
+        - MONGODB_ENVIRONMENT=replicaset
+    - stage: unified
+      node_js: 4
+      env:
+        - MONGODB_VERSION=4.2.x
+        - MONGODB_UNIFIED_TOPOLOGY=1
+        - MONGODB_ENVIRONMENT=sharded
 
     - stage: client-encryption
       node_js: 4