Unit Test: Disable IPv6 on Travis CI

Currently IPv6 on Travis is broken, and there are already a lot of
error reports:
https://github.com/travis-ci/travis-ci/issues/8711#issuecomment-343658967

Disable IPv6 build for the moment, otherwise all builds allways fail.

.travis.yml

@@ -81,7 +81,7 @@ before_script:
     -DCIVETWEB_SSL_OPENSSL_API_1_1=${OPENSSL_1_1}
     -DCIVETWEB_ENABLE_WEBSOCKETS=${ENABLE_WEBSOCKETS}
     -DCIVETWEB_ENABLE_CXX=${ENABLE_CXX}
-    -DCIVETWEB_ENABLE_IPV6=${ENABLE_IPV6}
+    -DCIVETWEB_ENABLE_IPV6=NO # ${ENABLE_IPV6} Disabled, see https://github.com/travis-ci/travis-ci/issues/8711#issuecomment-343658967
     -DCIVETWEB_ENABLE_SERVER_STATS=${ENABLE_SERVER_STATS}
     -DCIVETWEB_ENABLE_LUA=${ENABLE_LUA}
     -DCIVETWEB_ENABLE_LUA_SHARED=${ENABLE_LUA_SHARED}

src/civetweb.c

@@ -3096,9 +3096,8 @@ static char *
 mg_strndup_ctx(const char *ptr, size_t len, struct mg_context *ctx)
 {
 	char *p;
-	(
-	    void)ctx; /* Avoid Visual Studio warning if USE_SERVER_STATS is not
-                   * defined */
+    (void)ctx; /* Avoid Visual Studio warning if USE_SERVER_STATS is not
+                * defined */
 
 	if ((p = (char *)mg_malloc_ctx(len + 1, ctx)) != NULL) {
 		mg_strlcpy(p, ptr, len + 1);