Add lerna to package.json devDependencies

[Aliandi]

Fixes #774

Description

Even though it is necessary to have lerna installed globally to run commands such as npm i and npm run build, it is not listed on the devDependencies. This causes issues when trying to intall.
To avoid this, we added lerna as a devDependency on the package.json file.

Specific Changes

• Add the "lerna": "^3.2.1" line to the package.json

Testing

Before adding the line:

After adding the line:

[coveralls]

Pull Request Test Coverage Report for Build #2024

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.06%) to 87.441%

---

Files with Coverage Reduction	New Missed Lines	%
libraries/botframework-config/src/botConfigurationBase.ts	2	85.59%

Totals
Change from base Build #2023:	-0.06%
Covered Lines:	3004
Relevant Lines:	3306

---

💛 - Coveralls

[cleemullins]

This LGTM, but I would prefer @justinwilaby or @benbrown look before we merge.