[DatePicker] Fix lineHeight

Author: oliviertassinari

src/DatePicker/DayButton.js

@@ -38,6 +38,7 @@ function getStyles(props, context) {
       width: 41,
       padding: '4px 2px',
       opacity: disabled && '0.6',
+      lineHeight: 'inherit',
     },
     label: {
       position: 'relative',

src/DatePicker/YearButton.js

@@ -24,6 +24,7 @@ function getStyles(props, context) {
       width: 36,
       fontSize: 14,
       padding: '8px 2px',
+      lineHeight: 'inherit',
       color: year === new Date().getFullYear() && datePicker.color,
     },
     label: {