Update syntax in style.md

An apostrophe was missing from one word and placed in the wrong spot for another word. This PR adds and moves an apostrophe.

style.md

@@ -79,7 +79,7 @@ misnomer, since these conventions cover far more than just source file
 formatting—gofmt handles that for us.
 
 The goal of this guide is to manage this complexity by describing in detail the
-Dos and Don'ts of writing Go code at Uber. These rules exist to keep the code
+Do's and Dont's of writing Go code at Uber. These rules exist to keep the code
 base manageable while still allowing engineers to use Go language features
 productively.