feat(types): Add Typescript definitions. (#1676)

Fixes: #1670

Copies over the existing types and tests from DefinitelyTyped.
Includes updates to bring them up to date with 11.0

Remove `getTotalDelay` and `shouldPersist`, as they're considered private.

.travis.yml

@@ -32,7 +32,7 @@ jobs:
       node_js: lts/*
       env: linting
       # Show prettier errors, even if lint fails.
-      script: run-s --silent --continue-on-error lint prettier:check
+      script: run-s --silent --continue-on-error lint prettier:check dtslint
     - stage: test
       node_js: 12
     - node_js: 10

lib/interceptor.js

@@ -572,6 +572,10 @@ module.exports = class Interceptor {
     return this
   }
 
+  /**
+   * @private
+   * @returns {number}
+   */
   getTotalDelay() {
     return this.delayInMs + this.delayConnectionInMs
   }

lib/scope.js

@@ -239,6 +239,10 @@ class Scope extends EventEmitter {
     return this
   }
 
+  /**
+   * @private
+   * @returns {boolean}
+   */
   shouldPersist() {
     return this._persist
   }