Link against libboost_regex correctly on travis

script/configure.sh

@@ -3,5 +3,17 @@
 set -e
 
 git submodule update --init
-externals/gyp/gyp tree_sitter.gyp --depth .
-externals/gyp/gyp tree_sitter.gyp --depth . --format=make
+externals/gyp/gyp tree_sitter.gyp --depth . --format=make $@
+
+if [ $1 == "-h" ]; then
+  cat <<-HELP
+
+Variables:
+
+-D USE_BOOST_REGEX - Use boost regex library for tests, not the built-in regex
+                     library. This is useful when linking against an older
+                     version of the standard library. libboost_regex must be
+                     installed.
+
+HELP
+fi