Update to Kotlin 1.5

Appendices/Java Interoperability/Examples/src/NPEOnPlatformType.kt

@@ -15,5 +15,5 @@ fun main() {
   capture {
     val zn: JTool = JTool.get(null) // [5]
   } eq "NullPointerException: " +
-    "JTool.get(null) must not be null"
+    "get(null) must not be null"
 }

build.gradle

@@ -1,5 +1,5 @@
 buildscript {
-    ext.kotlin_version = '1.4.0'
+    ext.kotlin_version = '1.5.20'
     repositories {
         mavenCentral()
     }
@@ -34,8 +34,8 @@ allprojects {
         compile "junit:junit:4.12"
 
         // Logging support for samples:
-        compile 'io.github.microutils:kotlin-logging:1.6.24'
-        compile 'org.slf4j:slf4j-simple:1.8.0-beta4'
+        compile 'io.github.microutils:kotlin-logging:2.0.10'
+        compile 'org.slf4j:slf4j-simple:1.7.32'
     }
     compileKotlin.destinationDir = compileJava.destinationDir
     compileKotlin {