fix: make sure --save-exact is converted correctly

Fixes armano2#7 

Funny how these things go. I reported the issue then I started fixing a similar issue for npm to pnpm for sapphiredev/documentation-plugins#80 and turns out this fix also works for npm to yarn

Example regexr: regexr.com/6phbp

src/npmToYarn.ts

@@ -8,7 +8,7 @@ const npmToYarnTable = {
     let ret = command
       .replace('install', 'add')
       .replace('--save-dev', '--dev')
-      .replace(/\s*--save/, '')
+      .replace(/\s*--save(?!-)/, '')
       .replace('--no-package-lock', '--no-lockfile')
       .replace('--save-optional', '--optional')
       .replace('--save-exact', '--exact')
@@ -22,7 +22,7 @@ const npmToYarnTable = {
     let ret = command
       .replace('uninstall', 'remove')
       .replace('--save-dev', '--dev')
-      .replace(/\s*--save/, '')
+      .replace(/\s*--save(?!-)/, '')
       .replace('--no-package-lock', '--no-lockfile')
     if (/ -(?:-global|g)(?![^\b])/.test(ret)) {
       ret = ret.replace(/ -(?:-global|g)(?![^\b])/, '')