Add SB Curated (copied from the smartbugs repository).

dataset/arithmetic/integer_overflow_mapping_sym_1.sol

@@ -0,0 +1,18 @@
+/*
+ * @source: https://github.com/SmartContractSecurity/SWC-registry/blob/master/test_cases/integer_overflow_and_underflow/integer_overflow_mapping_sym_1.sol
+ * @author: -
+ * @vulnerable_at_lines: 16
+ */
+
+//Single transaction overflow
+
+pragma solidity ^0.4.11;
+
+contract IntegerOverflowMappingSym1 {
+    mapping(uint256 => uint256) map;
+
+    function init(uint256 k, uint256 v) public {
+        // <yes> <report> ARITHMETIC
+        map[k] -= v;
+    }
+}