qt,wallet: Fix a few typos in messages

As reported by [yahoe.001](https://www.transifex.com/user/profile/yahoe.001/).

src/qt/bitcoinstrings.cpp

@@ -191,7 +191,7 @@ QT_TRANSLATE_NOOP("bitcoin-core", ""
 "included in share/rpcuser. This option can be specified multiple times"),
 QT_TRANSLATE_NOOP("bitcoin-core", ""
 "Wallet will not create transactions that violate mempool chain limits "
-"(default: %u"),
+"(default: %u)"),
 QT_TRANSLATE_NOOP("bitcoin-core", ""
 "Warning: Unknown block versions being mined! It's possible unknown rules are "
 "in effect"),

src/qt/guiutil.cpp

@@ -961,11 +961,11 @@ QString formateNiceTimeOffset(qint64 secs)
     const int YEAR_IN_SECONDS = 31556952; // Average length of year in Gregorian calendar
     if(secs < 60)
     {
-        timeBehindText = QObject::tr("%n seconds(s)","",secs);
+        timeBehindText = QObject::tr("%n second(s)","",secs);
     }
     else if(secs < 2*HOUR_IN_SECONDS)
     {
-        timeBehindText = QObject::tr("%n minutes(s)","",secs/60);
+        timeBehindText = QObject::tr("%n minute(s)","",secs/60);
     }
     else if(secs < 2*DAY_IN_SECONDS)
     {

src/wallet/wallet.cpp

@@ -3399,7 +3399,7 @@ std::string CWallet::GetWalletHelpString(bool showDebug)
         strUsage += HelpMessageOpt("-dblogsize=<n>", strprintf("Flush wallet database activity from memory to disk log every <n> megabytes (default: %u)", DEFAULT_WALLET_DBLOGSIZE));
         strUsage += HelpMessageOpt("-flushwallet", strprintf("Run a thread to flush wallet periodically (default: %u)", DEFAULT_FLUSHWALLET));
         strUsage += HelpMessageOpt("-privdb", strprintf("Sets the DB_PRIVATE flag in the wallet db environment (default: %u)", DEFAULT_WALLET_PRIVDB));
-        strUsage += HelpMessageOpt("-walletrejectlongchains", strprintf(_("Wallet will not create transactions that violate mempool chain limits (default: %u"), DEFAULT_WALLET_REJECT_LONG_CHAINS));
+        strUsage += HelpMessageOpt("-walletrejectlongchains", strprintf(_("Wallet will not create transactions that violate mempool chain limits (default: %u)"), DEFAULT_WALLET_REJECT_LONG_CHAINS));
     }
 
     return strUsage;