fix: bring back the blank line between release notes sections

[AbdulrhmanGoni]

A one-liner that fixes #311

More context: conventional-changelog/conventional-changelog#1511 (comment)

@TimothyJones acknowledged this issue in #311 (comment), but looks like he forgot about it

[TimothyJones]

Thank you! Can we add a test so this doesn’t come back?

[AbdulrhmanGoni]

Thank you! Can we add a test so this doesn’t come back?
@TimothyJones

I see some existing unit tests in test/core.spec.js that could cover this, the tests currently expect a changelog to be joined with old changelogs without the blank line separator.

So I think we could just update those tests to expect a blank line separator between the new changelog and the old ones

Currently I see three tests like this:

commit-and-tag-version/test/core.spec.js

Lines 389 to 393 in 8094d6a

	verifyNewChangelogContentEquals({
	writeFileSyncSpy,
	expectedContent:
	frontMatter + '\n' + header + '\n' + changelog101 + changelog100,
	});

We can do something like this:

 verifyNewChangelogContentEquals({ 
   writeFileSyncSpy, 
   expectedContent: 
-    frontMatter + '\n' + header + '\n' + changelog101 + changelog100, 
+    frontMatter + '\n' + header + '\n' + changelog101 + '\n' + changelog100, 
 }); 

Update: I updated the three test cases like i showed above, what do you think @TimothyJones ?