Update TOML file indentation in .editorconfig (#998)

Cirq is using 4 space indentation in `pyproject.toml`. Let's follow
suit, to make things simpler.

Author: mhucka

.editorconfig

@@ -55,7 +55,7 @@ max_line_length = 88
 indent_size = 4
 
 [*.toml]
-indent_size = 2
+indent_size = 4
 
 [{*.yaml,*.yml,*.cff}]
 indent_size = 2