fix(spigot): update PlaceholderAPI dependency to 2.11.6

Their maven repo has been migrated and version 2.11.1 is no longer
available, causing builds to fail.

Author: diogotcorreia

triton-spigot/build.gradle

@@ -22,7 +22,7 @@ dependencies {
     compileOnly 'net.kyori:adventure-text-serializer-bungeecord:4.3.4'
 
     compileOnly 'com.comphenix.protocol:ProtocolLib:5.3.0-SNAPSHOT'
-    compileOnly 'me.clip:placeholderapi:2.11.1'
+    compileOnly 'me.clip:placeholderapi:2.11.6'
 
     // Libraries available on Spigot
     compileOnly 'org.fusesource.jansi:jansi:2.4.0' // Used for terminal translation