add test for #131

When diff starts in the first three lines

Closes #120

test/fixtures/first-three-line.diff

@@ -0,0 +1,18 @@
+commit fbf440dd9c32a60f9bc97693a6bd7b5ca87ec9fc
+Author: Steve Mao <maochenyan@gmail.com>
+Date:   Wed Mar 9 19:21:27 2016 +1100
+
+    0.6.2
+
+diff --git package.json package.json
+index 7379c98..3cba6ee 100644
+--- package.json
++++ package.json
+@@ -1,6 +1,6 @@
+ {
+   "name": "diff-so-fancy",
+-  "version": "0.6.1",
++  "version": "0.6.2",
+   "description": "Good-lookin' diffs with diff-highlight and more",
+   "bin": {
+     "diff-so-fancy": "diff-so-fancy",

test/header_clean.bats

@@ -63,6 +63,12 @@ output=$( load_fixture "file-moves" | $diff_so_fancy )
     refute_output --partial 'Use of uninitialized value'
 }
 
+@test "Hunk formatting: @@ -1,6 +1,6 @@" {
+	# stderr forced into output
+	output=$( load_fixture "first-three-line" | $diff_so_fancy )
+	assert_output --partial '@ package.json:3 @'
+}
+
 @test "mnemonicprefix handling" {
 	output=$( load_fixture "mnemonicprefix" | $diff_so_fancy )
 	assert_output --partial 'modified: test/header_clean.bats'