Update Travis CI - Perl versions and Mail::SPF dependency

- Bumped Perl supported versions
- Added Mail::SPF dependency. Zonemaster-Engine relies on Mail::SPF and there is a bug preventing its installation from cpanm. See Zonemaster-Engine commit `3ac72b0c` and/or pull request <zonemaster/zonemaster-engine#1287> for more information on this.

.travis.yml

@@ -3,10 +3,9 @@ dist: focal
 language: perl
 
 perl:
-    - "5.32"
-    - "5.30.2"
+    - "5.36"
+    - "5.30"
     - "5.26"
-    - "5.14.4"
 
 addons:
   apt:
@@ -26,6 +25,7 @@ addons:
     - liblist-moreutils-perl
     - liblocale-msgfmt-perl
     - libmail-rfc822-address-perl
+    - libmail-spf-perl
     - libmodule-find-perl
     - libnet-ip-perl
     - libpod-coverage-perl