try travis with perl 5.18 instead of 5.14

.travis.yml

@@ -16,11 +16,11 @@ matrix:
       env: BINDINGS=python CC=clang
     - compiler: gcc
       language: perl
-      perl: 5.14
+      perl: 5.18
       env: BINDINGS=perl
     - compiler: clang
       language: perl
-      perl: 5.14
+      perl: 5.18
       env: BINDINGS=perl CC=clang
 before_install:
   - sudo apt-get update -qq

src/bindings/perl/hammer.i

 %module hammer;
 %begin %{
 #include <unistd.h>
-#include <stdbool.h>
 #include <stdint.h>
 %}