Add period to LibratoConfig for librato-node (#42160)

types/librato-node/index.d.ts

@@ -26,6 +26,7 @@ export interface LibratoConfig {
     prefix?: string;
     source?: string;
     requestOptions?: LibratoRequestOptions;
+    period?: number;
     simulate?: false;
 }
 

types/librato-node/librato-node-tests.ts

@@ -26,6 +26,7 @@ librato.configure({
         method: 'POST',
         uri: 'https://foo.com',
     },
+    period: 5000,
     simulate: false,
 });