Upgrade to Facebook Graph API 2.8

v2.8 will be available till April 18, 2019 so users will have enough
time to upgrade to version 3 of Spring Social with support of the most
up to date Facebook API version

Fixes spring-attic#241 and spring-attic#217

spring-social-facebook/src/main/java/org/springframework/social/facebook/api/User.java

@@ -291,7 +291,9 @@ public String getAbout() {
 	 * The user's bio.
 	 * Available only with "user_about_me" permission for the authenticated user.
 	 * @return the user's bio, if available.
+	 * @deprecated this field is deprecated in Facebook API and always returns null, use the {@link #getAbout()} field instead.
 	 */
+	@Deprecated
 	public String getBio() {
 		return bio;
 	}

spring-social-facebook/src/main/java/org/springframework/social/facebook/api/UserOperations.java

@@ -126,8 +126,8 @@ public interface UserOperations {
 	 */
 	PagedList<Reference> search(String query);
 
-	static final String[] PROFILE_FIELDS = {
-		"id", "about", "age_range", "bio", "birthday", "context", "cover", "currency", "devices", "education", "email", 
+	String[] PROFILE_FIELDS = {
+		"id", "about", "age_range", "birthday", "context", "cover", "currency", "devices", "education", "email",
 		"favorite_athletes", "favorite_teams", "first_name", "gender", "hometown", "inspirational_people", "installed", "install_type",
 		"is_verified", "languages", "last_name", "link", "locale", "location", "meeting_for", "middle_name", "name", "name_format", 
 		"political", "quotes", "payment_pricepoints", "relationship_status", "religion", "security_settings", "significant_other", 

spring-social-facebook/src/main/java/org/springframework/social/facebook/api/impl/FacebookTemplate.java

@@ -108,7 +108,7 @@ public class FacebookTemplate extends AbstractOAuth2ApiBinding implements Facebo
 
 	private String applicationNamespace;
 
-	private String apiVersion = "2.5";
+	private String apiVersion = "2.8";
 
 	/**
 	 * Create a new instance of FacebookTemplate.