fix(aerospike extension): turn off build in Travis due to image version

Base image (Ubuntu 18) is no supported by Aerospike.

Closes #2881

travis-build.sh

@@ -18,6 +18,7 @@ if [ -n "${PHP_VERSION}" ]; then
     if [ "${PHP_VERSION}" == "5.6" ]; then
         # Aerospike C Client SDK 4.0.7, Debian 9.6 is not supported
         # https://github.com/aerospike/aerospike-client-php5/issues/145
+        sed -i -- 's/WORKSPACE_INSTALL_AEROSPIKE=true/WORKSPACE_INSTALL_AEROSPIKE=false/g' .env
         sed -i -- 's/PHP_FPM_INSTALL_AEROSPIKE=true/PHP_FPM_INSTALL_AEROSPIKE=false/g' .env
     fi
     if [ "${PHP_VERSION}" == "7.3" ]; then