Support Unicode \digamma (#2010)

* Support Unicode \digamma

* Update screenshotter images

src/symbols.js

@@ -306,7 +306,7 @@ defineSymbol(math, ams, textord, "\u2138", "\\daleth", true);
 defineSymbol(math, ams, textord, "\u2137", "\\gimel", true);
 
 // AMS Greek
-defineSymbol(math, ams, textord, "\u03dd", "\\digamma");
+defineSymbol(math, ams, textord, "\u03dd", "\\digamma", true);
 defineSymbol(math, ams, textord, "\u03f0", "\\varkappa");
 
 // AMS Delimiters

test/katex-spec.js

@@ -3390,7 +3390,7 @@ describe("Unicode", function() {
 
     it("should build Greek capital letters", function() {
         expect("\u0391\u0392\u0395\u0396\u0397\u0399\u039A\u039C\u039D" +
-                "\u039F\u03A1\u03A4\u03A7").toBuild(strictSettings);
+                "\u039F\u03A1\u03A4\u03A7\u03DD").toBuild(strictSettings);
     });
 
     it("should build arrows", function() {

test/screenshotter/ss_data.yaml

@@ -137,7 +137,7 @@ Gathered: |
       y = \sum_{i=1}^n i
     \end{array}
 GreekLetters: \alpha\beta\gamma\omega
-GreekUnicode: \frac{αβγδεϵζηθϑικλμνξοπϖρϱςστυφϕχψω}{ΓΔΘΞΠΣΦΨΩ\mathbf{Ω}\mathbf{\Omega}}
+GreekUnicode: \frac{αβγδεϵζηθϑικλμνξοπϖρϱςστυφϕχψω}{ΓΔΘΞΠΣΦΨΩϝ\mathbf{Ω}\mathbf{\Omega}}
 GroupMacros:
     macros:
         \startExp: e^\bgroup