Fix parse-duration usage in cli

[priitlatt]

NPM package parse-duration version was bumped from 1.1.0 to 2.1.3 In PR #95 for CodePush CLI. This caused the build to fail with the following error:

% npm run build

> [email protected] build
> tsc

script/command-parser.ts:1321:21 - error TS2349: This expression is not callable.
  Type 'typeof import("/private/tmp/ms-code-push-server/cli/node_modules/parse-duration/index")' has no call signatures.

1321   return Math.floor(parseDuration(durationString));
                         ~~~~~~~~~~~~~


Found 1 error in script/command-parser.ts:1321

Changes in this PR update parse-duration usages in cli/script/command-parser.ts.