Escape schema name and table name because the query fails if they contain dots (#18)

Thank you for the PR

Author: dropsonic

src/Pomelo.Extensions.Caching.MySql/MySqlQueries.cs

@@ -52,7 +52,7 @@ internal class MySqlQueries
 		public MySqlQueries(string schemaName, string tableName)
 		{
 			var tableNameWithSchema = string.Format(
-				"{0}.{1}", DelimitIdentifier(schemaName), DelimitIdentifier(tableName));
+				"{0}.{1}", EscapeIdentifier(DelimitIdentifier(schemaName)), EscapeIdentifier(DelimitIdentifier(tableName)));
 
 			// when retrieving an item, we do an UPDATE first and then a SELECT
 			GetCacheItem = string.Format(UpdateCacheItemFormat + GetCacheItemFormat, tableNameWithSchema);
@@ -85,5 +85,10 @@ private string EscapeLiteral(string literal)
 		{
 			return literal.Replace("'", "''");
 		}
+
+		private string EscapeIdentifier(string identifier)
+		{
+			return $"`{identifier}`";
+		}
 	}
 }