docs(user-guide/environment-variables): unify description style

Author: rami3l

doc/user-guide/src/environment-variables.md

@@ -41,7 +41,7 @@
   Set to `auto` to use colors only in tty streams, to `always` to always enable colors,
   or to `never` to disable colors.
 
-- `RUSTUP_UNPACK_RAM` *unstable* (default free memory or 500MiB if unable to tell, min 210MiB). Caps the amount of
+- `RUSTUP_UNPACK_RAM` *unstable* (default: free memory or 500MiB if unable to tell, min 210MiB). Caps the amount of
   RAM `rustup` will use for IO tasks while unpacking.
 
 - `RUSTUP_NO_BACKTRACE`. Disables backtraces on non-panic errors even when
@@ -61,7 +61,7 @@
   symlink proxies and instead always use hardlinks. If you find this fixes
   a problem, then please report the issue on the [rustup issue tracker].
 
-- `RUSTUP_TERM_PROGRESS_WHEN` (defaults: `auto`). Controls whether progress bars are shown or not.
+- `RUSTUP_TERM_PROGRESS_WHEN` (default: `auto`). Controls whether progress bars are shown or not.
   Set to `always` to always enable progress bars, and to `never` to disable them.
 
 - `RUSTUP_TERM_WIDTH` (default: none). Allows to override the terminal width for progress bars.