Update gradle to 7.2 (from 4.10.3) and fix the build.gradle file

build.gradle

@@ -235,7 +235,7 @@ mixin {
 
 // add Distant Horizon's Core source folders
 sourceSets {
-    core {
+    main {
         java {
             srcDirs("core/src/main/java");
             srcDirs("core/src/main/resources")

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-7.2-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.10.3-bin.zip