Clean up the javadoc to pass java 8's doclint

By: Thinkofdeath <thinkofdeath@spigotmc.org>

paper-api/src/main/java/org/bukkit/projectiles/ProjectileSource.java

@@ -11,6 +11,7 @@ public interface ProjectileSource {
     /**
      * Launches a {@link Projectile} from the ProjectileSource.
      *
+     * @param <T> a projectile subclass
      * @param projectile class of the projectile to launch
      * @return the launched projectile
      */
@@ -20,6 +21,7 @@ public interface ProjectileSource {
      * Launches a {@link Projectile} from the ProjectileSource with an
      * initial velocity.
      *
+     * @param <T> a projectile subclass
      * @param projectile class of the projectile to launch
      * @param velocity the velocity with which to launch
      * @return the launched projectile