Make class fields final

This reduces the probability of mutability issues.

Author: darxriggs

src/main/java/org/jenkinsci/plugins/bitbucket/BitbucketBuildStatusNotifier.java

@@ -56,10 +56,10 @@ public class BitbucketBuildStatusNotifier extends Notifier {
 
     private static final Logger logger = Logger.getLogger(BitbucketBuildStatusNotifier.class.getName());
 
-    private boolean notifyStart;
-    private boolean notifyFinish;
-    private boolean overrideLatestBuild;
-    private String credentialsId;
+    private final boolean notifyStart;
+    private final boolean notifyFinish;
+    private final boolean overrideLatestBuild;
+    private final String credentialsId;
 
     @DataBoundConstructor
     public BitbucketBuildStatusNotifier(final boolean notifyStart, final boolean notifyFinish,

src/main/java/org/jenkinsci/plugins/bitbucket/api/BitbucketApiService.java

@@ -34,8 +34,8 @@ public class BitbucketApiService extends OAuth20ServiceImpl {
     private static final String GRANT_TYPE_KEY = "grant_type";
     private static final String GRANT_TYPE_CLIENT_CREDENTIALS = "client_credentials";
 
-    private DefaultApi20 api;
-    private OAuthConfig config;
+    private final DefaultApi20 api;
+    private final OAuthConfig config;
 
     public BitbucketApiService(DefaultApi20 api, OAuthConfig config) {
         super(api, config);

src/main/java/org/jenkinsci/plugins/bitbucket/model/BitbucketBuildStatusResource.java

@@ -30,9 +30,9 @@ public class BitbucketBuildStatusResource {
 
     private static final String API_ENDPOINT = "https://api.bitbucket.org/2.0/";
 
-    private String owner;
-    private String repoSlug;
-    private String commitId;
+    private final String owner;
+    private final String repoSlug;
+    private final String commitId;
 
     public BitbucketBuildStatusResource(String owner, String repoSlug, String commitId) {
         this.owner = owner;