[LIT] Correcting max-failures option in lit documentation.

Author: Mike Edwards

llvm/docs/CommandGuide/lit.rst

@@ -158,11 +158,10 @@ EXECUTION OPTIONS
 SELECTION OPTIONS
 -----------------
 
-.. option:: --max-failures MAX_FAILURES
+.. option:: --max-failures N
 
- Stop execution after the given number of failures.
- An integer argument may be passed on the command line
- or the environment vairable MAX_FAILURES may be set
+ Stop execution after the given number ``N`` of failures.
+ An integer argument should be passed on the command line
  prior to execution.
 
 .. option:: --max-tests=N