Fixed .travis.yml

.travis.yml

@@ -1,11 +1,11 @@
 language: perl
 perl:
-   - 5.20
-   - 5.18
-   - 5.16
-   - 5.14
-   - 5.12
-   - 5.10
+   - '5.20'
+   - '5.18'
+   - '5.16'
+   - '5.14'
+   - '5.12'
+   - '5.10'
 matrix:
    fast_finish: true
 before_install: