Replaced some words (#5877)

Summary:
improved Vocabulary
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5877

Differential Revision: D17753217

Pulled By: anand1976

fbshipit-source-id: f255418534297e537a2735f0a0546c724b8f7c70

README.md

@@ -9,11 +9,11 @@ It is built on earlier work on [LevelDB](https://github.com/google/leveldb) by S
 and Jeff Dean (jeff@google.com)
 
 This code is a library that forms the core building block for a fast
-key value server, especially suited for storing data on flash drives.
+key-value server, especially suited for storing data on flash drives.
 It has a Log-Structured-Merge-Database (LSM) design with flexible tradeoffs
 between Write-Amplification-Factor (WAF), Read-Amplification-Factor (RAF)
 and Space-Amplification-Factor (SAF). It has multi-threaded compactions,
-making it specially suitable for storing multiple terabytes of data in a
+making it especially suitable for storing multiple terabytes of data in a
 single database.
 
 Start with example usage here: https://github.com/facebook/rocksdb/tree/master/examples