Add Cirrus CI for FreeBSD tests ✨ (#678)

- Add .cirrus.yml
- Update libnghttp2 to fix "undefined symbol
  nghttp2_option_set_max_outbound_ack" when running node
- Skip downloading Electron because it doesn't support FreeBSD.
  To achieve that we need Electron v7 beta which introduces a
  ELECTRON_SKIP_BINARY_DOWNLOAD environment variable.
  See: electron/electron#17627
- Use "npm i --unsafe-perm" because scripts run as root

.cirrus.yml

@@ -0,0 +1,11 @@
+freebsd_instance:
+  image_family: freebsd-12-0
+
+task:
+  name: FreeBSD
+  provision_script:
+    - pkg install -y git libnghttp2 node npm
+  install_script:
+    - git submodule update --init --recursive
+    - env ELECTRON_SKIP_BINARY_DOWNLOAD=1 npm i --unsafe-perm
+  test_script: npm t

.npmignore

@@ -41,6 +41,7 @@ yarn.lock
 .dntrc
 .gitmodules
 .travis.yml
+.cirrus.yml
 appveyor.yml
 
 # Unknown

README.md

@@ -5,6 +5,7 @@
 [![Node version](https://img.shields.io/node/v/leveldown.svg)](https://www.npmjs.com/package/leveldown)
 [![Travis](https://img.shields.io/travis/com/Level/leveldown.svg?logo=travis&label=)](https://travis-ci.com/Level/leveldown)
 [![AppVeyor](https://img.shields.io/appveyor/ci/Level/leveldown.svg?logo=appveyor&label=)](https://ci.appveyor.com/project/Level/leveldown)
+[![Cirrus CI](https://img.shields.io/cirrus/github/Level/leveldown?logo=cirrus-ci&label=)](https://cirrus-ci.com/github/Level/leveldown)
 [![npm](https://img.shields.io/npm/dm/leveldown.svg?label=dl)](https://www.npmjs.com/package/leveldown)
 [![Coverage Status](https://coveralls.io/repos/github/Level/leveldown/badge.svg)](https://coveralls.io/github/Level/leveldown)
 [![JavaScript Style Guide](https://img.shields.io/badge/code_style-standard-brightgreen.svg)](https://standardjs.com)

package.json

@@ -37,7 +37,7 @@
     "delayed": "^2.0.0",
     "dependency-check": "^4.1.0",
     "du": "^1.0.0",
-    "electron": "^6.0.0",
+    "electron": "~7.0.0-beta.1",
     "faucet": "^0.0.1",
     "glob": "^7.1.3",
     "hallmark": "^2.0.0",