fix: default line value

Author: yeonjuan

src/__fixtures__/unified

@@ -0,0 +1,6 @@
+diff --git a/test.txt b/test.txt
+index 27b30e2..62944e1 100644
+--- a/test.txt
++++ b/test.txt
+@@ -2,0 +3 @@ bbb
++ddd

src/__tests__/__snapshots__/unified.test.ts.snap

@@ -0,0 +1,34 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`unified parse \`unified 1`] = `
+{
+  "files": [
+    {
+      "chunks": [
+        {
+          "changes": [
+            {
+              "content": "ddd",
+              "lineAfter": 3,
+              "type": "AddedLine",
+            },
+          ],
+          "context": "bbb",
+          "fromFileRange": {
+            "lines": 0,
+            "start": 2,
+          },
+          "toFileRange": {
+            "lines": 1,
+            "start": 3,
+          },
+          "type": "Chunk",
+        },
+      ],
+      "path": "test.txt",
+      "type": "ChangedFile",
+    },
+  ],
+  "type": "GitDiff",
+}
+`;

src/__tests__/unified.test.ts

@@ -0,0 +1,10 @@
+import { getFixture } from './test-utils';
+import parseGitDiff from '../parse-git-diff';
+
+describe('unified', () => {
+  const fixture = getFixture('unified');
+
+  it('parse `unified', () => {
+    expect(parseGitDiff(fixture)).toMatchSnapshot();
+  });
+});

src/parse-git-diff.ts

@@ -280,7 +280,7 @@ function getRange(start: string, lines?: string) {
   const startNum = parseInt(start, 10);
   return {
     start: startNum,
-    lines: lines === undefined ? startNum : parseInt(lines, 10),
+    lines: lines === undefined ? 1 : parseInt(lines, 10),
   };
 }