Fixed broken build on VS 2012

git-svn-id: http://jsoncpp.svn.sourceforge.net/svnroot/jsoncpp/trunk@275 1f120ed1-78a5-a849-adca-83f0a9e25bb6
diff --git a/jsoncpp/src/test_lib_json/main.cpp b/jsoncpp/src/test_lib_json/main.cpp
index 1d89721..31f103c 100644
--- a/jsoncpp/src/test_lib_json/main.cpp
+++ b/jsoncpp/src/test_lib_json/main.cpp
@@ -992,7 +992,7 @@
    JSONTEST_ASSERT_STRING_EQUAL("-9.223372036854776e+18", normalizeFloatingPointStr(val.asString()));
 
    // 10^19
-   const uint64_t ten_to_19 = 1e19;
+   const Json::UInt64 ten_to_19 = static_cast<Json::UInt64>( 1e19 );
    val = Json::Value(Json::UInt64(ten_to_19));
 
    JSONTEST_ASSERT_EQUAL(Json::uintValue, val.type());