Update error message for tabulations in source code.

RELNOTES: None.
PiperOrigin-RevId: 210117808

src/main/java/com/google/devtools/build/lib/syntax/Lexer.java

diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Lexer.java b/src/main/java/com/google/devtools/build/lib/syntax/Lexer.java
index bcda4e3..5507053 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Lexer.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Lexer.java
@@ -286,7 +286,7 @@
       } else if (c == '\r') {
         pos++;
       } else if (c == '\t') {
-        error("Tabulations are not allowed for identation. Use spaces instead.");
+        error("Tab characters are not allowed for indentation. Use spaces instead.");
         indentLen++;
         pos++;
       } else if (c == '\n') { // entirely blank line: discard

src/test/java/com/google/devtools/build/lib/syntax/LexerTest.java

diff --git a/src/test/java/com/google/devtools/build/lib/syntax/LexerTest.java b/src/test/java/com/google/devtools/build/lib/syntax/LexerTest.java
index 379d955..33a66d1 100644
--- a/src/test/java/com/google/devtools/build/lib/syntax/LexerTest.java
+++ b/src/test/java/com/google/devtools/build/lib/syntax/LexerTest.java
@@ -380,7 +380,7 @@
   @Test
   public void testIndentationWithTab() throws Exception {
     tokens("def x():\n\tpass");
-    assertThat(lastError.toString()).contains("Tabulations are not allowed");
+    assertThat(lastError).contains("Tab characters are not allowed");
   }
 
   @Test