Corrected and expanded Input component ref handling

Renamed `inputRef` to `ref` (as this is the correct prop name), and also expanded on the ref-handling code example in order to use more supported React standards, as `this.refs` is deprecated.

Author: rorz

README.md

@@ -260,12 +260,16 @@ import { Input } from 'react-chat-elements'
             text='Send'/>
     }/>
 
-// clear text eg:
+// Clear text, e.g.:
+// For pure components, use inputRef instead of this.inputRef
+
+inputRef = React.createRef();
+// ...
 <Input
-    ref='input'
+    ref={el => (this.inputRef = el)}
     placeholder="Type here..."/>
-
-this.refs.input.clear();
+// ...
+this.inputRef.clear();
 ```
 
 #### Input props
@@ -283,7 +287,7 @@ this.refs.input.clear();
 | inputStyle | none | object | inputStyle object |
 | leftButtons | none | object(component) | left buttons component |
 | rightButtons | none | object(component) | right buttons component |
-| inputRef | none | function | input or textarea ref |
+| ref | none | function | input or textarea ref |
 | maxlength | none | int | input or textarea maxlength |
 | onMaxLengthExceed | none | function | called when max length exceed |
 | autofocus | false | bool | input autofocus |
@@ -523,4 +527,4 @@ import { SpotifyMessage } from 'react-chat-elements'
 | view | list | string | spotify view type (list or coverart) |
 | data | {} | object | message data |
 | width | 300 | int | spotify embed width |
-| height | 380 | int | spotify embed height |
+| height | 380 | int | spotify embed height |