Merge branch 'brodybits-stryker-3-update' (...)

Note that the Stryker Mutator 3.1.0 update was done by first
removing version 2.5.0, in order to update the transitive
dependencies in yarn.lock.

Author: Christopher J. Brody

package.json

@@ -55,10 +55,9 @@
     "update-notifier": "^4.1.0"
   },
   "devDependencies": {
-    "@stryker-mutator/core": "^2.5.0",
-    "@stryker-mutator/html-reporter": "^2.5.0",
-    "@stryker-mutator/javascript-mutator": "^2.5.0",
-    "@stryker-mutator/jest-runner": "^2.5.0",
+    "@stryker-mutator/core": "^3.1.0",
+    "@stryker-mutator/javascript-mutator": "^3.1.0",
+    "@stryker-mutator/jest-runner": "^3.1.0",
     "eslint": "^6.4.0",
     "eslint-config-standard": "^14.1.0",
     "eslint-plugin-import": "^2.18.2",