Fix typo (Part of Issue #217)

Author: mtrofin

docs/regalloc-demo/demo.md

@@ -12,7 +12,7 @@ In this demo we will look at:
 Set up some environment variables according to where you want to clone/build
 all of the code:
 ```bash
-export WORKINGD_DIR=~
+export WORKING_DIR=~
 ```
 
 Change the directory to wherever you'd like to put everything.
@@ -554,4 +554,4 @@ Now, you should have a build of clang in `$WORKING_DIR/llvm-release-build/bin` t
 you can use to compile projects using the ML regalloc eviction heuristic.
 To compile with the ML regalloc eviction heuristic, all you need to do
 is make sure to pass the `-mllvm -regalloc-enable-advisor=release` flag
-to `clang` whenever you're compiling something.
+to `clang` whenever you're compiling something.