Try updating travis config

Author: thomasjm

.travis.yml

@@ -76,6 +76,14 @@ matrix:
     compiler: ": #stack 8.6.5"
     addons: {apt: {packages: [libgmp-dev]}}
 
+  - env: BUILD=stack ARGS="--stack-yaml stack-9.0.2-aeson1.yaml"
+    compiler: ": #stack 9.0.2 (Aeson 1)"
+    addons: {apt: {packages: [libgmp-dev]}}
+
+  - env: BUILD=stack ARGS="--stack-yaml stack-9.0.2-aeson2.yaml"
+    compiler: ": #stack 9.0.2 (Aeson 2)"
+    addons: {apt: {packages: [libgmp-dev]}}
+
   # Nightly builds are allowed to fail
   - env: BUILD=stack ARGS="--resolver nightly"
     compiler: ": #stack nightly"