[dependency]: bump bitcoinjs-lib from 6.1.0 to 6.1.5 in /nanowallet

Bumps [bitcoinjs-lib](https://github.com/bitcoinjs/bitcoinjs-lib) from 6.1.0 to 6.1.5.
- [Changelog](https://github.com/bitcoinjs/bitcoinjs-lib/blob/master/CHANGELOG.md)
- [Commits](bitcoinjs/bitcoinjs-lib@v6.1.0...v6.1.5)

---
updated-dependencies:
- dependency-name: bitcoinjs-lib
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

nanowallet/package-lock.json

@@ -24,7 +24,7 @@
     "babel-preset-es2015": "^6.3.13",
     "babelify": "^7.2.0",
     "bip32-path": "^0.4.2",
-    "bitcoinjs-lib": "^6.1.0",
+    "bitcoinjs-lib": "^6.1.5",
     "bootstrap": "3.4.1",
     "browser-sync": "^2.29.1",
     "browserify": "^13.0.0",