bump bytecode to v2.15.13

Author: pelikhan

bytecode/bytecode.md

@@ -21,7 +21,7 @@ For a more highlevel description of runtime and bytecode, see [Runtime implement
 
     img_version_major = 2
     img_version_minor = 15
-    img_version_patch = 12
+    img_version_patch = 13
     img_version = $version
     magic0 = 0x53766544 // "DevS"
     magic1 = 0xf1296e0a