Update .editorconfig to align with rustfmt. (libp2p#162)

The current settings differ from rustfmt which is used during CI runs to
check the source code format. In particular, rustfmt will replace tabs
with spaces, therefore this commit attempts to use the same settings
already for editing.

.editorconfig

@@ -1,10 +1,9 @@
 root = true
 [*]
-indent_style=tab
-indent_size=tab
-tab_width=4
+indent_style=space
+indent_size=4
 end_of_line=lf
 charset=utf-8
 trim_trailing_whitespace=true
-max_line_length=120
-insert_final_newline=true
+max_line_length=100
+insert_final_newline=false