Update bignumber.js to 7.2.1

fixes #2206

Author: dougwilson

Changes.md

@@ -4,6 +4,11 @@ This file is a manually maintained list of changes for each release. Feel free
 to add your changes here when sending pull requests. Also send corrections if
 you spot any mistakes.
 
+## HEAD
+
+* Update `bignumber.js` to 7.2.1 #2206
+  - Fix npm deprecation warning
+
 ## v2.17.0 (2019-04-17)
 
 * Add reverse type lookup for small performance gain #2170

package.json

@@ -13,7 +13,7 @@
   ],
   "repository": "mysqljs/mysql",
   "dependencies": {
-    "bignumber.js": "6.0.0",
+    "bignumber.js": "7.2.1",
     "readable-stream": "2.3.6",
     "safe-buffer": "5.1.2",
     "sqlstring": "2.3.1"