stack-collapse -> stack_collapse in README

Fix naming

Author: tmandry

stack_collapse/README.md

@@ -7,15 +7,15 @@ stack-collapse is a tool to produce [Flame Graph](https://github.com/brendangreg
 ```bash
 $ # Install stack_collapse if you haven't done so yet.
 
-$ cargo install --git https://github.com/rust-lang/measureme stack-collapse
+$ cargo install --git https://github.com/rust-lang/measureme stack_collapse
 
 $ git clone https://github.com/rust-lang/regex.git
 
 $ cd regex
 
 $ cargo rustc -- -Z self-profile
 
-$ stack-collapse regex-{pid}
+$ stack_collapse regex-{pid}
 
 $ ../path/to/FlameGraph/flamegraph.pl out.stacks_folded > rustc.svg