Set javadoc encoding to UTF-8 (#1168)

* specify java doc encoding

* Update build.gradle

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Co-authored-by: Bogdan Kobylynskyi <[email protected]>

Author: matsudamper

build.gradle

@@ -65,6 +65,7 @@ codeCoverageReport.dependsOn test
 
 compileJava.options.encoding = "UTF-8"
 compileTestJava.options.encoding = "UTF-8"
+javadoc.options.encoding = "UTF-8"
 
 java {
     withJavadocJar()