feat(structuredPatch): Handle default context option

Author: Kiougar

src/patch/create.js

@@ -2,7 +2,10 @@ import {diffLines} from '../diff/line';
 
 export function structuredPatch(oldFileName, newFileName, oldStr, newStr, oldHeader, newHeader, options) {
   if (!options) {
-    options = { context: 4 };
+    options = {};
+  }
+  if (!options.context) {
+    options.context = 4;
   }
 
   const diff = diffLines(oldStr, newStr, options);