Update prefixes.js

Author: Marukome0743

data/prefixes.js

@@ -475,7 +475,7 @@ let prefixPlaceholder = require('caniuse-lite/data/features/css-placeholder')
 
 f(prefixPlaceholder, browsers => {
   prefix(['::placeholder'], {
-    browsers,
+    browsers: browsers.concat(['ie 10 old', 'ie 11 old', 'firefox 18 old']),
     feature: 'css-placeholder',
     selector: true
   })
@@ -486,7 +486,7 @@ let prefixPlaceholderShown = require('caniuse-lite/data/features/css-placeholder
 
 f(prefixPlaceholderShown, browsers => {
   prefix([':placeholder-shown'], {
-    browsers: browsers.concat(['firefox 50 old']),
+    browsers,
     feature: 'css-placeholder-shown',
     selector: true
   })