fix inconsistent updates to react component state

Executions of setState() may be batched, and so updates to this.state and
this.props can be asynchronous, so references to this.state and this.props
should not be made in the new state, and instead the callback form of
setState() should be used.

These alerts were found using lgtm.com:
https://lgtm.com/projects/g/BoostIO/Boostnote/alerts/?mode=tree&ruleFocus=1819283066

see: https://reactjs.org/docs/state-and-lifecycle.html#state-updates-may-be-asynchronous

Author: s0

browser/components/SnippetTab.js

@@ -55,10 +55,10 @@ class SnippetTab extends React.Component {
         this.handleRename()
         break
       case 27:
-        this.setState({
-          name: this.props.snippet.name,
+        this.setState((prevState, props) => ({
+          name: props.snippet.name,
           isRenaming: false
-        })
+        }))
         break
     }
   }

browser/main/Detail/SnippetNoteDetail.js

@@ -368,11 +368,11 @@ class SnippetNoteDetail extends React.Component {
         name: mode
       })
     }
-    this.setState({note: Object.assign(this.state.note, {snippets: snippets})})
+    this.setState(state => ({note: Object.assign(state.note, {snippets: snippets})}))
 
-    this.setState({
-      note: this.state.note
-    }, () => {
+    this.setState(state => ({
+      note: state.note
+    }), () => {
       this.save()
     })
   }
@@ -381,11 +381,11 @@ class SnippetNoteDetail extends React.Component {
     return (e) => {
       const snippets = this.state.note.snippets.slice()
       snippets[index].mode = name
-      this.setState({note: Object.assign(this.state.note, {snippets: snippets})})
+      this.setState(state => ({note: Object.assign(state.note, {snippets: snippets})}))
 
-      this.setState({
-        note: this.state.note
-      }, () => {
+      this.setState(state => ({
+        note: state.note
+      }), () => {
         this.save()
       })
 
@@ -399,10 +399,10 @@ class SnippetNoteDetail extends React.Component {
     return (e) => {
       const snippets = this.state.note.snippets.slice()
       snippets[index].content = this.refs['code-' + index].value
-      this.setState({note: Object.assign(this.state.note, {snippets: snippets})})
-      this.setState({
-        note: this.state.note
-      }, () => {
+      this.setState(state => ({note: Object.assign(state.note, {snippets: snippets})}))
+      this.setState(state => ({
+        note: state.note
+      }), () => {
         this.save()
       })
     }
@@ -597,17 +597,17 @@ class SnippetNoteDetail extends React.Component {
   }
 
   jumpNextTab () {
-    this.setState({
-      snippetIndex: (this.state.snippetIndex + 1) % this.state.note.snippets.length
-    }, () => {
+    this.setState(state => ({
+      snippetIndex: (state.snippetIndex + 1) % state.note.snippets.length
+    }), () => {
       this.focusEditor()
     })
   }
 
   jumpPrevTab () {
-    this.setState({
-      snippetIndex: (this.state.snippetIndex - 1 + this.state.note.snippets.length) % this.state.note.snippets.length
-    }, () => {
+    this.setState(state => ({
+      snippetIndex: (state.snippetIndex - 1 + state.note.snippets.length) % state.note.snippets.length
+    }), () => {
       this.focusEditor()
     })
   }