fix single quote literal

```
Welcome to Scala 2.12.6 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_172).
Type in expressions for evaluation. Or try :help.

scala> '''
<console>:12: warning: deprecated syntax for character literal (use '\'' for single quote)
       '''
       ^
res0: Char = '
```

Author: xuwei-k

src/main/scala/scala/tools/refactoring/sourcegen/SourceUtils.scala

@@ -46,9 +46,9 @@ trait SourceUtils {
     def currentCharsAreMultilineCommentCommentStart = current2CharsAre('/', '*')
     def currentCharsAreMultilineCommentCommentEnd = current2CharsAre('*', '/')
     def currentCharIsRegularQuote = currentCharIs('"')
-    def currentCharsAreSingleQuotedSingleQuote = current3CharsAre(''', ''', ''')
-    def currentCharsAreEscapedSingleQuote = current2CharsAre('\\', ''')
-    def currentCharIsSingleQuote = currentCharIs(''')
+    def currentCharsAreSingleQuotedSingleQuote = current3CharsAre('\'', '\'', '\'')
+    def currentCharsAreEscapedSingleQuote = current2CharsAre('\\', '\'')
+    def currentCharIsSingleQuote = currentCharIs('\'')
     def currentCharsAreEscapedRegularQuote = current2CharsAre('\\', '"')
     def currentCharIsNewline = currentCharIs('\n')
     def currentCharIsBackTick = currentCharIs('`')

src/main/scala/scala/tools/refactoring/util/SourceWithMarker.scala

@@ -605,7 +605,7 @@ object SourceWithMarker {
     }
 
     val delimiter = charOfClass { c =>
-      c == '`' || c == ''' || c == '"' || c == '.' || c == ';' || c == ','
+      c == '`' || c == '\'' || c == '"' || c == '.' || c == ';' || c == ','
     }
 
     val opChar = charOfClass { c =>
@@ -620,10 +620,10 @@ object SourceWithMarker {
     }
 
     val characterLiteral = {
-      val charEscape = character('b') | 't' | 'n' | 'f' | 'r' | '"' | ''' | '\\'
+      val charEscape = character('b') | 't' | 'n' | 'f' | 'r' | '"' | '\'' | '\\'
       val octEscape = octalDigit ~ octalDigit.atMostNtimes(2)
 
-      ''' ~ ((any.butNot('\\') | ('\\' ~ (charEscape | octEscape)))) ~ '''
+      '\'' ~ ((any.butNot('\\') | ('\\' ~ (charEscape | octEscape)))) ~ '\''
     }
 
     val stringLiteral = {
@@ -680,7 +680,7 @@ object SourceWithMarker {
 
     val plainid = (upper ~ idrest) | varid | op
 
-    val symbolLiteral = ''' ~ plainid
+    val symbolLiteral = '\'' ~ plainid
 
     val literalIdentifier = '`' ~ any.butNot('`').atLeastOnce ~ '`'