build: sort sources alphabetically

The header files in the sources list are sorted alphabetically but not
the c++ source code files. This commit sorts the c++ source code file
names.

PR-URL: nodejs#10892
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: James M Snell <jasnell@gmail.com>

node.gyp

@@ -145,17 +145,13 @@
       ],
 
       'sources': [
-        'src/tracing/agent.cc',
-        'src/tracing/node_trace_buffer.cc',
-        'src/tracing/node_trace_writer.cc',
-        'src/tracing/trace_event.cc',
-        'src/debug-agent.cc',
         'src/async-wrap.cc',
-        'src/env.cc',
-        'src/fs_event_wrap.cc',
         'src/cares_wrap.cc',
         'src/connection_wrap.cc',
         'src/connect_wrap.cc',
+        'src/debug-agent.cc',
+        'src/env.cc',
+        'src/fs_event_wrap.cc',
         'src/handle_wrap.cc',
         'src/js_stream.cc',
         'src/node.cc',
@@ -178,6 +174,7 @@
         'src/node_zlib.cc',
         'src/node_i18n.cc',
         'src/pipe_wrap.cc',
+        'src/process_wrap.cc',
         'src/signal_wrap.cc',
         'src/spawn_sync.cc',
         'src/string_bytes.cc',
@@ -186,8 +183,11 @@
         'src/stream_wrap.cc',
         'src/tcp_wrap.cc',
         'src/timer_wrap.cc',
+        'src/tracing/agent.cc',
+        'src/tracing/node_trace_buffer.cc',
+        'src/tracing/node_trace_writer.cc',
+        'src/tracing/trace_event.cc',
         'src/tty_wrap.cc',
-        'src/process_wrap.cc',
         'src/udp_wrap.cc',
         'src/util.cc',
         'src/uv.cc',