Use bitcoin-kmp 0.21.0 (#89)

Author: sstone

pom.xml

@@ -171,12 +171,12 @@
         <dependency>
             <groupId>fr.acinq.bitcoin</groupId>
             <artifactId>bitcoin-kmp-jvm</artifactId>
-            <version>0.20.0</version>
+            <version>0.21.0</version>
         </dependency>
         <dependency>
             <groupId>fr.acinq.secp256k1</groupId>
             <artifactId>secp256k1-kmp-jni-jvm</artifactId>
-            <version>0.15.0</version>
+            <version>0.16.0</version>
         </dependency>
         <dependency>
             <groupId>org.scodec</groupId>