CTxMemPool::WriteFeeEstimates: fix version required to read

KomodoPlatform/komodo#523

After these changes version required to read in fee_estimates.dat
will be set to 0x111d4 (70100) by default, instead of wrong (legacy
codebase) 109900 value. So, the error ERROR: CTxMemPool::ReadFeeEstimates()
on wallet startup, mentioned above wouldn't appear.

Delete of existing fee_estimates.dat before upgrade to the new version
of wallet with with commit included - also could be recommended.

src/txmempool.cpp

@@ -776,7 +776,7 @@ CTxMemPool::WriteFeeEstimates(CAutoFile& fileout) const
 {
     try {
         LOCK(cs);
-        fileout << 109900; // version required to read: 0.10.99 or later
+        fileout << 70100; // version required to read: 0.7.1.0 or later
         fileout << CLIENT_VERSION; // version that wrote the file
         minerPolicyEstimator->Write(fileout);
     }