license: revert license file change

Since 'http' is used in the license text itself,
we should probably just leave it as is.

PR #272

UNLICENSE

@@ -21,4 +21,4 @@ OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 OTHER DEALINGS IN THE SOFTWARE.
 
-For more information, please refer to <https://unlicense.org/>
+For more information, please refer to <http://unlicense.org/>