Fix FileAlreadyExistsException after server upgrade (fixes #50)

Author: MrMicky-FR

build.gradle

@@ -1,6 +1,6 @@
 allprojects {
     group 'com.azuriom'
-    version '1.3.7'
+    version '1.3.8'
 }
 
 subprojects {

bukkit/src/main/java/com/azuriom/azlink/bukkit/injector/NettyLibraryLoader.java

@@ -49,7 +49,7 @@ private void loadLibrary(String groupId, String artifactId, String version) thro
         Path jar = this.libsFolder.resolve(artifactId + "-" + version + ".jar");
 
         if (!Files.exists(jar)) {
-            Files.createDirectory(jar.getParent());
+            Files.createDirectories(jar.getParent());
 
             this.plugin.getLogger().warn("Downloading " + artifactId + " v" + version + "...");