Fix typo

src/script/sigcache.cpp

@@ -45,7 +45,7 @@ public:
     {
         // DoS prevention: limit cache size to less than 10MB
         // (~200 bytes per cache entry times 50,000 entries)
-        // Since there are a maximum of 20,000 signature operations per block
+        // Since there is a maximum of 20,000 signature operations per block
         // 50,000 is a reasonable default.
         int64_t nMaxCacheSize = GetArg("-maxsigcachesize", 50000);
         if (nMaxCacheSize <= 0) return;