build(deps): bump maven-source-plugin from 3.0.1 to 3.2.1 (twilio#538)

Bumps [maven-source-plugin](https://github.com/apache/maven-source-plugin) from 3.0.1 to 3.2.1.
- [Release notes](https://github.com/apache/maven-source-plugin/releases)
- [Commits](apache/maven-source-plugin@maven-source-plugin-3.0.1...maven-source-plugin-3.2.1)

pom.xml

@@ -87,7 +87,7 @@
           <plugin>
             <groupId>org.apache.maven.plugins</groupId>
             <artifactId>maven-source-plugin</artifactId>
-            <version>3.0.1</version>
+            <version>3.2.1</version>
             <executions>
               <execution>
                 <id>attach-sources</id>
@@ -271,7 +271,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-source-plugin</artifactId>
-        <version>3.1.0</version>
+        <version>3.2.1</version>
         <executions>
           <execution>
             <id>attach-sources</id>