Update java-interop.md
Update java-interop.md

fixed syntax source.size is property, not method
JetBrains/kotlin-web-site,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,meilalina/kotlin-web-site,meilalina/kotlin-web-site,madvirus/kotlin-web-site,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,JetBrains/kotlin-web-site,hltj/kotlin-web-site-cn,madvirus/kotlin-web-site,hltj/kotlin-web-site-cn,meilalina/kotlin-web-site,JetBrains/kotlin-web-site,JetBrains/kotlin-web-site,JetBrains/kotlin-web-site,meilalina/kotlin-web-site,JetBrains/kotlin-web-site,madvirus/kotlin-web-site