httpserver: include deque

It seems gcc 9.2.0 requires deque to be included:

  x86_64-pc-linux-gnu-g++ -std=c++11 -DHAVE_CONFIG_H -I. -I../src/config   -I. -I./obj -I/usr/include/db5.1/ -pthread -I/usr/include -I./leveldb/include -I./leveldb/helpers/memenv   -I./secp256k1/include    -pthread -I/usr/include/db5.1 -DHAVE_BUILD_INFO -D__STDC_FORMAT_MACROS    -march=native -O2 -pipe -fomit-frame-pointer -c -o libdogecoin_server_a-httpserver.o `test -f 'httpserver.cpp' || echo './'`httpserver.cpp
  httpserver.cpp:71:10: error: ‘deque’ in namespace ‘std’ does not name a template type
     71 |     std::deque<std::unique_ptr<WorkItem>> queue;
        |          ^~~~~
  httpserver.cpp:30:1: note: ‘std::deque’ is defined in header ‘<deque>’; did you forget to ‘#include <deque>’?
     29 | #include <event2/keyvalq_struct.h>
    +++ |+#include <deque>
     30 |
  httpserver.cpp: In member function ‘bool WorkQueue<WorkItem>::Enqueue(WorkItem*)’:
  httpserver.cpp:110:13: error: ‘queue’ was not declared in this scope; did you mean ‘Enqueue’?
    110 |         if (queue.size() >= maxDepth) {
        |             ^~~~~
        |             Enqueue
  httpserver.cpp:113:9: error: ‘queue’ was not declared in this scope; did you mean ‘Enqueue’?
    113 |         queue.emplace_back(std::unique_ptr<WorkItem>(item));
        |         ^~~~~
        |         Enqueue
  httpserver.cpp: In member function ‘void WorkQueue<WorkItem>::Run()’:
  httpserver.cpp:125:35: error: ‘queue’ was not declared in this scope; did you mean ‘Enqueue’?
    125 |                 while (running && queue.empty())
        |                                   ^~~~~
        |                                   Enqueue
  httpserver.cpp:129:31: error: ‘queue’ was not declared in this scope; did you mean ‘Enqueue’?
    129 |                 i = std::move(queue.front());
        |                               ^~~~~
        |                               Enqueue
  httpserver.cpp: In member function ‘size_t WorkQueue<WorkItem>::Depth()’:
  httpserver.cpp:154:16: error: ‘queue’ was not declared in this scope; did you mean ‘Enqueue’?
    154 |         return queue.size();
        |                ^~~~~
        |                Enqueue

src/httpserver.cpp

@@ -19,6 +19,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <signal.h>
+#include <deque>
 #include <future>
 
 #include <event2/event.h>