third_party: fix typo (#685)

Co-authored-by: Alexey Alexandrov <aalexand@users.noreply.github.com>
diff --git a/third_party/d3flamegraph/README.md b/third_party/d3flamegraph/README.md
index 94055d2..eb84b68 100644
--- a/third_party/d3flamegraph/README.md
+++ b/third_party/d3flamegraph/README.md
@@ -25,7 +25,7 @@
 
 ## Old version of d3-pprof
 
-A previous verison of d3-flame-graph bundled for pprof used Rollup instead of
+A previous version of d3-flame-graph bundled for pprof used Rollup instead of
 Webpack. This has now been migrated directly into this directory.
 
 The repository configuring Rollup was here: