feat: make reqwest an optional dependency (#979)

Cargo.toml

@@ -21,7 +21,8 @@ is-it-maintained-open-issues = { repository = "starship/starship" }
 maintenance = { status = "actively-developed" }
 
 [features]
-default = ["battery"]
+default = ["battery", "http"]
+http = ["reqwest"]
 
 [dependencies]
 clap = "2.33.0"
@@ -52,7 +53,7 @@ urlencoding = "1.0.0"
 open = "1.3.4"
 # OpenSSL causes problems when building a MUSL release. Opting to use native SSL implementation
 # see: https://github.com/richfelker/musl-cross-make/issues/65#issuecomment-509790889
-reqwest = { version = "0.10.4", default-features = false, features = ["blocking", "rustls-tls"] }
+reqwest = { version = "0.10.4", default-features = false, optional = true, features = ["blocking", "rustls-tls"] }
 unicode-width = "0.1.7"
 textwrap = "0.11.0"
 term_size = "0.3.1"