Options settable tests to use a different special charactor

Summary: Something changed and the special charactor seems to be conflict with an exisitng value. Change it to unblock the build.

Test Plan: Run the test and make sure it passes

Reviewers: kradhakrishnan

Reviewed By: kradhakrishnan

Subscribers: leveldb, andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D55845

util/options_test.cc

@@ -1489,7 +1489,7 @@ TEST_F(OptionsParserTest, EscapeOptionString) {
 // string on limited platforms as it depends on behavior of compilers.
 #ifdef OS_LINUX
 #ifndef __clang__
-const char kSpecialChar = 'R';
+const char kSpecialChar = 'z';
 typedef std::vector<std::pair<int, size_t>> OffsetGap;
 
 void FillWithSpecialChar(char* start_ptr, size_t total_size,