clang-tidy: use raw string literals

Found with modernize-raw-string-literals

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/TDB2.cpp

@@ -992,7 +992,7 @@ void TDB2::revert_backlog (
   const std::string& current,
   const std::string& prior)
 {
-  std::string uuid_att = "\"uuid\":\"" + uuid + '"';
+  std::string uuid_att = R"("uuid":")" + uuid + '"';
 
   bool found = false;
   for (auto task = b.rbegin (); task != b.rend (); ++task)

src/Task.cpp

@@ -1010,9 +1010,9 @@ std::string Task::composeJSON (bool decorate /*= false*/) const
           out << ',';
 
         Datetime d (i.first.substr (11));
-        out << "{\"entry\":\""
+        out << R"({"entry":")"
             << d.toISO ()
-            << "\",\"description\":\""
+            << R"(","description":")"
             << json::encode (i.second)
             << "\"}";