Fixed typo in CLI error reporting

include/internal/catch_commandline.hpp

@@ -51,7 +51,7 @@ namespace Catch {
             ss << seed;
             ss >> config.rngSeed;
             if( ss.fail() )
-                throw std::runtime_error( "Argment to --rng-seed should be the word 'time' or a number" );
+                throw std::runtime_error( "Argument to --rng-seed should be the word 'time' or a number" );
         }
     }
     inline void setVerbosity( ConfigData& config, int level ) {