Update the license short code (#174)

Use the official code
https://spdx.org/licenses/BSD-3-Clause.html

Fixes #173

README.md

@@ -14,7 +14,7 @@ The backport should be referred to using the "ThreeTen" name.
 Active development on JSR-310 is at [OpenJDK](http://openjdk.java.net/):
 
 This GitHub repository is a fork of that originally used to create JSR-310.
-That repository used the same BSD 3-clause license as this repository.
+That repository used the same BSD-3-Clause license as this repository.
 
 Issues about the backport should be reported here at GitHub.
 Pull requests and issues will only be considered so far as matching the behaviour

pom.xml

@@ -114,7 +114,7 @@
   <!-- ==================================================================== -->
   <licenses>
     <license>
-      <name>BSD 3-clause</name>
+      <name>BSD-3-Clause</name>
       <url>https://raw.githubusercontent.com/ThreeTen/threetenbp/main/LICENSE.txt</url>
       <distribution>repo</distribution>
     </license>

src/site/markdown/index.md

@@ -10,7 +10,7 @@ use the JSR-310 API on Java SE 6 and 7.
 The backport should be referred to using the "ThreeTen" name.
 The backport is curated by the primary author of the Java 8 date and time library, [Stephen Colebourne](https://www.joda.org/).
 
-ThreeTen-Backport is licensed under the business-friendly [BSD 3-clause license](license.html).
+ThreeTen-Backport is licensed under the business-friendly [BSD-3-Clause license](license.html).
 
 
 ## <i></i> Features