Added constructor signatures to java.io.FileReader and java.io.FileWriter since there are safe methods with Charset that can be used since java 11. (#152)

Thanks, I merged this in. Will do a few more tests, but looks fine.
There will be a new release soon, as Java 13 comes out.

Author: aspan

src/main/resources/de/thetaphi/forbiddenapis/signatures/jdk-unsafe-1.6.txt

@@ -23,8 +23,14 @@ java.lang.String#<init>(byte[],int,int)
 java.lang.String#<init>(byte[],int,int,int)
 java.lang.String#getBytes()
 java.lang.String#getBytes(int,int,byte[],int) 
-java.io.FileReader
-java.io.FileWriter
+java.io.FileReader#<init>(java.lang.String)
+java.io.FileReader#<init>(java.io.File)
+java.io.FileReader#<init>(java.io.FileDescriptor)
+java.io.FileWriter#<init>(java.lang.String)
+java.io.FileWriter#<init>(java.lang.String,boolean)
+java.io.FileWriter#<init>(java.io.File)
+java.io.FileWriter#<init>(java.io.File,boolean)
+java.io.FileWriter#<init>(java.io.FileDescriptor)
 java.io.ByteArrayOutputStream#toString()
 java.io.InputStreamReader#<init>(java.io.InputStream)
 java.io.OutputStreamWriter#<init>(java.io.OutputStream)