Upgrade blevesearch to v0.8.1 (#9177)

For #1441

https://github.com/blevesearch/bleve/commit/a91b427b59b893f112021841ba7370d285f8426f

vendor/github.com/RoaringBitmap/roaring/clz.go

@@ -0,0 +1,11 @@
+// +build go1.9
+// "go1.9", from Go version 1.9 onward
+// See https://golang.org/pkg/go/build/#hdr-Build_Constraints
+
+package roaring
+
+import "math/bits"
+
+func countLeadingZeros(x uint64) int {
+	return bits.LeadingZeros64(x)
+}