Bugfix: Trivial: RPC: getblockchaininfo help: pruneheight is the lowest, not highest, block

src/rpc/blockchain.cpp

@@ -892,7 +892,7 @@ UniValue getblockchaininfo(const UniValue& params, bool fHelp)
             "  \"verificationprogress\": xxxx, (numeric) estimate of verification progress [0..1]\n"
             "  \"chainwork\": \"xxxx\"     (string) total amount of work in active chain, in hexadecimal\n"
             "  \"pruned\": xx,             (boolean) if the blocks are subject to pruning\n"
-            "  \"pruneheight\": xxxxxx,    (numeric) heighest block available\n"
+            "  \"pruneheight\": xxxxxx,    (numeric) lowest-height complete block stored\n"
             "  \"softforks\": [            (array) status of softforks in progress\n"
             "     {\n"
             "        \"id\": \"xxxx\",        (string) name of softfork\n"