Increase the resolution of default timebase

The old value 1000 was too low, which caused the effective duration and
frame rate calculation to have an 1% error for typical 30 frame/second
inputs. Symptom of the issue has been that most 2 pass encodings were
undershooting target bit rate by 1% or so for 30 fps input.

Change-Id: Ice204e86f844ceb9ce973456f2b995cc095283cf

vpxenc.c

diff --git a/vpxenc.c b/vpxenc.c
index 45ec7e5..032e2e8 100644
--- a/vpxenc.c
+++ b/vpxenc.c
@@ -1188,7 +1188,7 @@
     /* Change the default timebase to a high enough value so that the encoder
      * will always create strictly increasing timestamps.
      */
-    cfg.g_timebase.den = 1000;
+    cfg.g_timebase.den = 100000;
 
     /* Never use the library's default resolution, require it be parsed
      * from the file or set on the command line.