[Docs] Remove hard tab character from code block in optbisect documentation

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@338105 91177308-0d34-0410-b5e6-96231b3b80d8

docs/OptBisect.rst

@@ -166,7 +166,7 @@ A MachineFunctionPass should use FunctionPass::skipFunction() as such:
 
   bool MyMachineFunctionPass::runOnMachineFunction(Function &MF) {
     if (skipFunction(*MF.getFunction())
-	  return false;
+      return false;
     // Otherwise, run the pass normally.
   }