[gitattributes] add whitespace checks to *.sh files
[gitattributes] add whitespace checks to *.sh files

Update the .gitattributes file to add whitespace checks to all *.sh
files. This is done specifically to enfore that shell files are indented
with tabs instead of spaces since things like heredocs break if a file
is indented with spaces.

libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,libra/libra,aptos-labs/aptos-core,libra/libra