Apply suggestions from code review

Co-authored-by: Camelid <camelidcamel@gmail.com>
Co-authored-by: lzutao <15225902+lzutao@users.noreply.github.com>

Author: 3 people

posts/2021-02-11-Rust-1.50.0.md

@@ -25,7 +25,7 @@ from the appropriate page on our website, and check out the
 
 ## What's in 1.50.0 stable
 
-For this release, we have improved array indexing, expanded union field safety, refined file descriptors, and new library additions.
+For this release, we have improved array indexing, expanded union field safety, refined file descriptors, and added to the standard library.
 See the [detailed release notes][notes] to learn about other changes
 not covered by this post.
 
@@ -63,7 +63,7 @@ assignments to these fields as well.
 
 ### A niche for `File` on Unix platforms
 
-Some types in Rust have specific limitations on what is considered
+Some types in Rust have specific limitations on what is considered a
 valid value, which may not cover the entire range of possible memory
 values. We call any remaining invalid value a [niche], and this space
 may be used for type layout optimizations. For example, in Rust 1.28
@@ -76,7 +76,7 @@ as well because it can never be `-1`! System calls which return a file
 descriptor use `-1` to indicate that an error occurred (check `errno`)
 so it's never possible for `-1` to be a real file descriptor. Starting
 in Rust 1.50 this niche is represented to the compiler so it can be
-use in layout optimizations too. It follows that `Option<File>` will
+used in layout optimizations too. It follows that `Option<File>` will
 now have the same size as `File` itself!
 
 [niche]: https://rust-lang.github.io/unsafe-code-guidelines/glossary.html#niche