internal/murmur: fix appengine and s390x (#1419)

internal/murmur/murmur_appengine.go

@@ -1,11 +1,11 @@
-// +build appengine
+// +build appengine s390x
 
 package murmur
 
 import "encoding/binary"
 
 func getBlock(data []byte, n int) (int64, int64) {
-	k1 := binary.LittleEndian.Int64(data[n*16:])
-	k2 := binary.LittleEndian.Int64(data[(n*16)+8:])
+	k1 := int64(binary.LittleEndian.Uint64(data[n*16:]))
+	k2 := int64(binary.LittleEndian.Uint64(data[(n*16)+8:]))
 	return k1, k2
 }

internal/murmur/murmur_unsafe.go

@@ -1,4 +1,5 @@
 // +build !appengine
+// +build !s390x
 
 package murmur