patch 8.1.0729: there is a SourcePre autocommand event but not a SourcePost

Problem:    There is a SourcePre autocommand event but not a SourcePost.
Solution:   Add the SourcePost autocommand event. (closes #3739)
diff --git a/src/fileio.c b/src/fileio.c
index fd8fd24..929cc15 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -7795,8 +7795,9 @@
     {"SessionLoadPost",	EVENT_SESSIONLOADPOST},
     {"ShellCmdPost",	EVENT_SHELLCMDPOST},
     {"ShellFilterPost",	EVENT_SHELLFILTERPOST},
-    {"SourcePre",	EVENT_SOURCEPRE},
     {"SourceCmd",	EVENT_SOURCECMD},
+    {"SourcePre",	EVENT_SOURCEPRE},
+    {"SourcePost",	EVENT_SOURCEPOST},
     {"SpellFileMissing",EVENT_SPELLFILEMISSING},
     {"StdinReadPost",	EVENT_STDINREADPOST},
     {"StdinReadPre",	EVENT_STDINREADPRE},