revert pprof upgrade

Author: Stephan Dilly

Cargo.lock

@@ -56,7 +56,7 @@ which = "4.2"
 
 # pprof is not available on windows
 [target.'cfg(not(windows))'.dependencies]
-pprof = { version = "0.6", features = ["flamegraph"], optional = true }
+pprof = { version = "=0.6.1", features = ["flamegraph"], optional = true }
 
 [dev-dependencies]
 pretty_assertions = "1.0"