Pin icu_calendar to v2.1 (#704)

We should pin to this version since we're using unstable features from
`icu_calendar`.

Author: jedel1043

Cargo.toml

@@ -45,7 +45,7 @@ web-time = "1.1.0"
 
 # ICU4X
 tinystr = "0.8.0"
-icu_calendar = { version = "2.1.0", default-features = false, features = ["unstable"] }
+icu_calendar = { version = "~2.1.0", default-features = false, features = ["unstable"] }
 icu_locale_core = "2.1.0"
 zerovec = "0.11.0"
 databake = "0.2.0"