swig 3 seems to work for perl, so let's try the backport

.travis.yml

@@ -104,8 +104,7 @@ before_install:
   - sudo apt-get update -qq
   - sudo apt-get install -y lcov
   - gem install coveralls-lcov
-  - if [ "$BINDINGS" != "none" ]; then sudo apt-get install -yqq swig; fi
-  - if [ "$BINDINGS" == "perl" ]; then sudo add-apt-repository ppa:dns/irc -y; sudo apt-get update -qq; sudo apt-get install -yqq swig=2.0.8-1irc1~12.04; fi
+  - if [ "$BINDINGS" != "none" ]; then sudo apt-get install -yqq swig/trusty-backports; fi
   - if [ "$BINDINGS" == "python" ]; then sudo apt-get install -yqq python-dev; fi
   - if [ "$BINDINGS" == "dotnet" ]; then sudo add-apt-repository ppa:directhex/monoxide -y; sudo apt-get update -qq; sudo apt-get install -yqq mono-devel mono-mcs nunit nunit-console; mozroots --import --sync; fi
 install: true