fix(toml): Don't error on leading whitespace in infostring

According to the [RFC](https://rust-lang.github.io/rfcs/3503-frontmatter.html):

> Opens with 3+ dashes followed by 0+ whitespace,
> an optional term (one or more characters excluding whitespace and commas),
> 0+ whitespace, and a newline

Author: epage

src/cargo/util/toml/embedded.rs

@@ -245,7 +245,7 @@ fn split_source(input: &str) -> CargoResult<Source<'_>> {
         _ => source.content.split_at(fence_end),
     };
     let (info, content) = rest.split_once("\n").unwrap_or((rest, ""));
-    let info = info.trim_end();
+    let info = info.trim();
     if !info.is_empty() {
         source.info = Some(info);
     }
@@ -373,7 +373,7 @@ Ok(
     Source {
         shebang: None,
         info: Some(
-            " cargo",
+            "cargo",
         ),
         frontmatter: Some(
             "[dependencies]\ntime=\"0.1.25\"\n",