Update 20mb artifact limit to 40mb

Author: benvinegar

docs/sourcemaps.rst

@@ -363,7 +363,7 @@ If you upload artifacts **after** an error is captured by Sentry, Sentry will no
 Verify your source files are not too large
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-For an individual artifact, Sentry accepts a max filesize of **20 MB**.
+For an individual artifact, Sentry accepts a max filesize of **40 MB**.
 
 Often users hit this limit because they are transmitting source files at an interim build stage. For example, after Webpack/Browserify has combined all
 your source files, but before minification has taken place. If possible, send the original source files.