license: fix up MIT license so it's an exact match

Before:

```console
$ licensee diff --license mit LICENSE-MIT
Comparing to MIT License:
Input Length:      1092
License length:    1020
Similarity:      92.46%
diff --git a/LICENSE b/LICENSE
index 0ce42af..be0ff1c 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,3 +1,4 @@
{+spack project developers. see the top-level copyright file for details.+}
permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "software"), to deal in
the software without restriction, including without limitation the rights to
```

After:

```console
$ licensee diff --license mit LICENSE-MIT
Comparing to MIT License:
Input Length:       1020
License length:     1020
Similarity:      100.00%
Exact match!
```

This gets us a 100% license match from GitHub's `licensee` tool.

0 files changed, 0 insertions, 0 deletions