Fix copy-paste bug in HitsPerSlabStrategy::exportConfig()

Summary: `exportConfig()` was reporting `config_.minSlabs` for the `num_slabs_free_mem` key instead of `config_.numSlabsFreeMem`. This meant monitoring would show the wrong value for this config field

Reviewed By: AlnisM

Differential Revision: D104298706

fbshipit-source-id: e7c800f31bd62ce7591d815f00f6ba1d07ac4b08

Author: IvanTopolcic

cachelib/allocator/HitsPerSlabStrategy.h

@@ -118,15 +118,16 @@ class HitsPerSlabStrategy : public RebalanceStrategy {
 
   // Exports configuration as a string map for monitoring.
   std::map<std::string, std::string> exportConfig() const override {
-    return {{"rebalancer_type", folly::sformat("{}", getTypeString())},
-            {"min_slabs", folly::sformat("{}", config_.minSlabs)},
-            {"num_slabs_free_mem", folly::sformat("{}", config_.minSlabs)},
-            {"min_lru_tail_age", folly::sformat("{}", config_.minLruTailAge)},
-            {"max_lru_tail_age", folly::sformat("{}", config_.maxLruTailAge)},
-            {"diff_ratio", folly::sformat("{}", config_.diffRatio)},
-            {"min_diff", folly::sformat("{}", config_.minDiff)},
-            {"eviction_age_map",
-             evictionAgeMapToStr(config_.classIdTargetEvictionAge.get())}};
+    return {
+        {"rebalancer_type", folly::sformat("{}", getTypeString())},
+        {"min_slabs", folly::sformat("{}", config_.minSlabs)},
+        {"num_slabs_free_mem", folly::sformat("{}", config_.numSlabsFreeMem)},
+        {"min_lru_tail_age", folly::sformat("{}", config_.minLruTailAge)},
+        {"max_lru_tail_age", folly::sformat("{}", config_.maxLruTailAge)},
+        {"diff_ratio", folly::sformat("{}", config_.diffRatio)},
+        {"min_diff", folly::sformat("{}", config_.minDiff)},
+        {"eviction_age_map",
+         evictionAgeMapToStr(config_.classIdTargetEvictionAge.get())}};
   }
 
  protected: