add .npmrc to use exact versions

[mrjones2014]

• [x] Related GitHub issue(s) linked in PR description
• [x] Destination branch merged, built and tested with your changes
• [x] Code formatted and follows best practices and patterns
• [x] Code builds cleanly (no additional warnings or errors)
• [x] Manually tested
• [x] Automated tests are passing
• [x] No decreases in automated test coverage
• [x] Documentation updated (readme, docs, comments, etc.)
• [x] Localization: No hard-coded error messages in code files (minimally in string constants) Fixes #51