feat: drop react@15

BREAKING CHANGE: react 15 support is dropped

Author: nLight

.travis.yml

@@ -30,6 +30,5 @@ install:
   - ./install_react.sh
 env:
   matrix:
-    - REACT_VERSION=15.6
     - REACT_VERSION=16.7
     - REACT_VERSION=16.8

install_react.sh

@@ -1,5 +1,4 @@
 #!/bin/bash
 
-if [ "$REACT_VERSION" = "15.6" ]; then npm install react@15.6 react-dom@15.6; fi
 if [ "$REACT_VERSION" = "16.7" ]; then npm install react@16.7 react-dom@16.7; fi
 if [ "$REACT_VERSION" = "16.8" ]; then npm install react@16.8 react-dom@16.8; fi