add ripgrep to travis ci cache directories list

CI often fails for the github api rate limit when downloading ripgrep
package. This workaroud is trying to enable Travis CI cache of the
ripgrep package and lower the failure rate.

Signed-off-by: tom-shan <swt0008411@163.com>

.travis.yml

@@ -9,6 +9,7 @@ cache:
 # All directories need to be listed here, because Travis does not support globs.
 # Auto generated by scripts/prepare-travis
 # start_cache_directories
+  - /tmp/vscode-ripgrep-cache-1.2.4
   - dev-packages/application-manager/node_modules
   - dev-packages/application-package/node_modules
   - dev-packages/electron/node_modules

scripts/prepare-travis

@@ -36,6 +36,14 @@ for (const name in workspaces) {
     }
 }
 
+const ripgrepVersions = child_process.execSync('yarn list --pattern vscode-ripgrep | grep -o "vscode-ripgrep@.*" | cut -d @ -f 2')
+    .toString().trim().split(os.EOL);
+for (const i in ripgrepVersions) {
+    const rv = ripgrepVersions[i];
+    const ripgrepPath = '/tmp/vscode-ripgrep-cache-' + rv;
+    directories.push(ripgrepPath);
+}
+
 const travisPath = path.resolve(__dirname, '../.travis.yml');
 const content = fs.readFileSync(travisPath).toString();
 const startIndex = content.indexOf('# start_cache_directories') + '# start_cache_directories'.length;