travis: Pin fixtures for Puppet 4

.fixtures.puppet4.yml

@@ -0,0 +1,17 @@
+fixtures:
+  forge_modules:
+    stdlib:
+      repo: puppetlabs/stdlib
+      ref: 5.2.0
+    concat:
+      repo: puppetlabs/concat
+      ref: 5.3.0
+    vcsrepo:
+      repo: puppetlabs/vcsrepo
+      ref: 2.4.0
+    apt:
+      repo: puppetlabs/apt
+      ref: 6.3.0
+    zypprepo: puppet/zypprepo
+  symlinks:
+    icingaweb2: "#{source_dir}"

.travis.yml

@@ -12,7 +12,7 @@ matrix:
   - rvm: '2.4'
     env: PUPPET_VERSION="~> 5.0" CHECK=build DEPLOY_TO_FORGE=yes
   - rvm: '2.1'
-    env: PUPPET_VERSION="~> 4.0" CHECK=test
+    env: PUPPET_VERSION="~> 4.0" CHECK=test FIXTURES_YML=.fixtures.puppet4.yml
   - rvm: '2.4'
     env: PUPPET_VERSION="~> 5.0" CHECK=test
   - rvm: '2.5'