dashboard: increase notification log to 200 lines

The go command lists all packages that were built.
A recent breakage notification included this text:

$ tail -100 < log
ok      errors
ok      exp/ebnf
?       exp/ebnflint [no test files]
ok      exp/gotype
ok      exp/norm
ok      exp/spdy

If the breakage occurred before this point it would
not be visible in the output.

R=golang-dev, gri, kevlar
CC=golang-dev
https://golang.org/cl/5504109

misc/dashboard/app/build/notify.txt

@@ -5,5 +5,5 @@ http://{{.Hostname}}/log/{{.Result.LogHash}}
 
 http://code.google.com/p/go/source/detail?r={{shortHash .Commit.Hash}}
 
-$ tail -100 < log
-{{printf "%s" .Log.Text | tail 100}}
+$ tail -200 < log
+{{printf "%s" .Log.Text | tail 200}}