Fix grammar in README.md

"it's" is a contraction of "it is". The possessive pronoun of "its"
should be used instead in this context

Signed-off-by: Remy Suen <remy.suen@gmail.com>

Author: rcjsuen

README.md

@@ -1,6 +1,6 @@
 # Bash Language Server
 
-Bash language server implementation based on [Tree Sitter][tree-sitter] and it's
+Bash language server implementation based on [Tree Sitter][tree-sitter] and its
 [grammar for Bash][tree-sitter-bash].
 
 ## Features