Sync .clang-format file with main ROOT repo

Author: guitargeek

.clang-format

@@ -10,6 +10,7 @@ AlignTrailingComments: true
 AllowAllParametersOfDeclarationOnNextLine: true
 AllowShortBlocksOnASingleLine: Never
 AllowShortCaseLabelsOnASingleLine: true
+AllowShortEnumsOnASingleLine: false
 AllowShortFunctionsOnASingleLine: Inline
 AllowShortIfStatementsOnASingleLine: false
 AllowShortLoopsOnASingleLine: false
@@ -78,7 +79,7 @@ SpacesInContainerLiterals: true
 SpacesInCStyleCastParentheses: false
 SpacesInParentheses: false
 SpacesInSquareBrackets: false
-Standard:        c++11
+Standard:        c++17
 TabWidth:        3
 UseTab:          Never