[core] Fix compilation failure caused by compilation warning for gcc 8

When compiling with gcc 8.3 under linux, I've got compiler error caused
by the following warning:
../src/mbgl/util/chrono.cpp:26:26: error: ‘__builtin___snprintf_chk’ output may be truncated before the last format character [-Werror=format-truncation=]
I need to slightly increase the buffer size to get rid of the warning.

1 files changed, 7 insertions, 2 deletions

diff --git a/src/mbgl/util/chrono.cpp b/src/mbgl/util/chrono.cpp
index 6674e73c42..03e97eedf5 100644
--- a/src/mbgl/util/chrono.cpp
+++ b/src/mbgl/util/chrono.cpp
@@ -22,8 +22,13 @@ std::string rfc1123(Timestamp timestamp) {
     std::time_t time = std::chrono::system_clock::to_time_t(timestamp);
     std::tm info;
     _gmtime(&time, &info);
-    char buffer[30];
-    snprintf(buffer, 30, "%s, %02d %s %4d %02d:%02d:%02d GMT", week[info.tm_wday], info.tm_mday,
+
+    // Buffer size 30 is OK assuming the year has 4 digits. However, In theory, it might have
+    // more digits. Under gcc 8.3.0 with -Os optimization flag, there is compiler warning
+    // complaining about the buffer size might be too small. Inceasing the buffer to 32 fixes
+    // the warning.
+    char buffer[32];
+    snprintf(buffer, 32, "%s, %02d %s %4d %02d:%02d:%02d GMT", week[info.tm_wday], info.tm_mday,
              months[info.tm_mon], 1900 + info.tm_year, info.tm_hour, info.tm_min, info.tm_sec);
     return buffer;
 }