add special case for Homebrew; test on osx

.travis.yml

@@ -1,4 +1,9 @@
+os:
+  - linux
+  - osx
 language: node_js
 node_js:
   - '10'
   - '8'
+before_install:
+  - if [[ ${TRAVIS_OS_NAME} == "osx" ]]; then brew install "node@${TRAVIS_NODE_VERSION}" && export PKG_CONFIG_PATH="/usr/local/opt/icu4c/lib/pkgconfig" && nvm use system; fi;

index.js

@@ -20,6 +20,11 @@ const defaultNpmPrefix = (() => {
 		return path.dirname(process.execPath);
 	}
 
+	// Homebrew special case; always assume /usr/local
+	if (process.execPath.startsWith('/usr/local/Cellar/node')) {
+		return '/usr/local';
+	}
+
 	// `/usr/local/bin/node` → `prefix=/usr/local`
 	return path.dirname(path.dirname(process.execPath));
 })();