Use monospace font for diff hunks

Fixes misalignment issues and makes width of line numbers bar more
consistent.

Author: Tunous

app/src/main/java/com/gh4a/adapter/timeline/DiffViewHolder.java

@@ -128,11 +128,11 @@ public void bind(TimelineItem.Diff item) {
             appendLineNumber(builder, maxLineLength, rightLineText, rightLine, item, true);
 
             // Add additional padding between line numbers and code
-            builder.append("  ");
+            builder.append(" ");
 
             int lineNumberLength = builder.length() - spanStart;
 
-            builder.append("  ").append(lines[i]).append("  ");
+            builder.append(" ").append(lines[i]).append(" ");
             if (i < lines.length - 1) {
                 builder.append("\n");
             }
@@ -159,11 +159,11 @@ private void appendLineNumber(SpannableStringBuilder builder, int maxLength, Str
         int start = builder.length();
 
         // Add padding at the start of text
-        builder.append("    ");
+        builder.append("  ");
 
         // Right align the number if necessary
         for (int i = 0; i < maxLength - numberText.length(); i++) {
-            builder.append("  ");
+            builder.append(" ");
         }
 
         builder.append(numberText);

app/src/main/res/layout/row_timeline_diff.xml

@@ -29,6 +29,7 @@
             android:id="@+id/diff_hunk"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
+            android:fontFamily="monospace"
             android:paddingBottom="@dimen/code_diff_padding"
             android:paddingTop="@dimen/code_diff_padding"
             android:textColor="?android:attr/textColorPrimary"