[2.1.x] Templates-Compiler project is missing a dependency on scala-compiler

While looking for a solution for Issue #1419 I tried to compile and test the Templates-Compiler project as follows:

```
$ sbt
$ project Templates-Compiler
$ test
```

Compilation failed because of missing `scala.tools.nsc` package. So it seems that `templatesCompilerDependencies` in `Build.scala` is missing the following dependency:
```
"org.scala-lang"                    %    "scala-compiler"           %   buildScalaVersion,
```