Fix logic for OS check

Author: jmikola

.travis.scripts/debug-core.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 
-if [ "${TRAVIS_OS_NAME}" != "osx" ]; then
+if [ "${TRAVIS_OS_NAME}" = "osx" ]; then
     # https://www.ics.uci.edu/~pattis/common/handouts/macmingweclipse/allexperimental/mac-gdb-install.html
     echo "Cannot debug core files on macOS: ${1}"
     exit 1