fix: add types for stablePatchmarks (#74)

* fix: add types for stablePatchmarks

* fix flow

Author: thymikee

index.d.ts

@@ -4,6 +4,7 @@ type DiffOptions = {
   expand?: boolean
   colors?: boolean
   contextLines?: number
+  stablePatchmarks?: boolean
   aAnnotation?: string
   bAnnotation?: string
 }

src/index.js

@@ -9,13 +9,14 @@ const prettyFormat = require('pretty-format');
 const { ReactElement } = prettyFormat.plugins;
 const reactElement = Symbol.for('react.element');
 
-type Options = {
+type Options = {|
   expand?: boolean,
   colors?: boolean,
   contextLines?: number,
+  stablePatchmarks?: boolean,
   aAnnotation?: string,
   bAnnotation?: string,
-};
+|};
 
 const defaultOptions = {
   expand: false,
@@ -30,7 +31,7 @@ const SNAPSHOT_TITLE = 'Snapshot Diff:\n';
 
 const snapshotDiff = (valueA: any, valueB: any, options?: Options): string => {
   let difference;
-  const mergedOptions = Object.assign({}, defaultOptions, options);
+  const mergedOptions = { ...defaultOptions, ...options };
 
   if (isReactComponent(valueA) && isReactComponent(valueB)) {
     difference = diffReactComponents(valueA, valueB, mergedOptions);