loose the assertion condition of rate_limiter_test

Summary: 0.9 can make the test flaky since just found one test fail with 0.88

Test Plan: make all check

Reviewers: sdong, andrewkr

Reviewed By: andrewkr

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D63939

util/rate_limiter_test.cc

@@ -87,8 +87,8 @@ TEST_F(RateLimiterTest, Rate) {
               arg.request_size - 1, target / 1024, rate / 1024,
               elapsed / 1000000.0);
 
-      ASSERT_GE(rate / target, 0.9);
-      ASSERT_LE(rate / target, 1.1);
+      ASSERT_GE(rate / target, 0.85);
+      ASSERT_LE(rate / target, 1.15);
     }
   }
 }