fix(install): don't fail install if debug logs are present

closes #173
- previously, `ghost install` would fail if there were debug log files
present in the install directory. This PR fixes it so log files don't
make the install exit

lib/commands/install.js

@@ -1,6 +1,7 @@
 'use strict';
 const fs = require('fs-extra');
 const path = require('path');
+const every = require('lodash/every');
 const Listr = require('listr');
 const Promise = require('bluebird');
 const symlinkSync = require('symlink-or-copy').sync;
@@ -55,7 +56,10 @@ module.exports.execute = function execute(version, options) {
         process.chdir(dir);
     }
 
-    if (fs.readdirSync(process.cwd()).length) {
+    let filesInDir = fs.readdirSync(process.cwd());
+
+    // Check if there are existing files that *aren't* ghost-cli debug log files
+    if (filesInDir.length && !every(filesInDir, (file) => file.match(/^ghost-cli-debug-.*\.log$/i))) {
         return Promise.reject(new errors.SystemError('Current directory is not empty, Ghost cannot be installed here.'));
     }