fix(travis): add 5.0.0 release to matrix

Author: duncdrum

.travis.yml

@@ -28,7 +28,7 @@ services:
 env:
   - img=existdb/existdb:latest
   - img=existdb/existdb:release
-  # - img= existdb/existdb:4.5.0
+  - img= existdb/existdb:4.7.1
   - img=evolvedbinary/exist-db:eXist-3.6.1-minimal
 
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