Merge pull request #63 from r-ralph/v1.8.1

Bump up version to 1.8.1

Author: r-ralph

buildSrc/src/main/kotlin/Consts.kt

@@ -1,5 +1,5 @@
 object Consts {
-    const val version = "1.8.0"
+    const val version = "1.8.1"
     const val groupId = "com.linecorp"
     const val artifactId = "apng"
     const val bintrayRepo = "apng-drawable"