.travis.yml: add more available perls

Use as much perls to test as possible.

Signed-off-by: Jens Rehsack <[email protected]>

Author: rehsack

.travis.yml

@@ -10,10 +10,15 @@ language: perl
 perl:
   - "5.30"
   - "5.28"
-  - "5.26"
   - "5.26-shrplib"
+  - "5.26"
+  - "5.24-shrplib"
   - "5.24"
   - "5.22"
+  - "5.20"
+  - "5.18"
+  - "5.16"
+  - "5.14"
 matrix:
   include:
     - perl: "5.30"