Enable IPv6 build with Travis

.travis.yml

@@ -17,7 +17,6 @@ env:
     - ENABLE_SSL_DYNAMIC_LOADING=YES
     - ENABLE_WEBSOCKETS=YES
     - ENABLE_CXX=NO
-    - ENABLE_IPV6=NO
     - ENABLE_LUA=NO
     - ENABLE_LUA_SHARED=NO
     - C_STANDARD=auto
@@ -25,12 +24,20 @@ env:
   matrix:
     - BUILD_SHARED=NO
       NO_FILES=NO
+      ENABLE_IPV6=NO
     - BUILD_SHARED=YES
       NO_FILES=NO
+      ENABLE_IPV6=NO
     - BUILD_SHARED=NO
       NO_FILES=YES
+      ENABLE_IPV6=NO
     - BUILD_SHARED=YES
       NO_FILES=YES
+      ENABLE_IPV6=NO
+    - BUILD_SHARED=NO
+      NO_FILES=NO
+      ENABLE_IPV6=YES
+
 
 addons:
   apt: