[docs] Fixed incorrect underlines

hpvm/docs/developerdocs/specifications/hetero-c.rst

 Hetero-C++ Language Specification
-===============================
+=================================
 
 A Hetero-C++ program consists of Parallel Sections, Parallel Tasks, and
 Parallel Loops. Parallel Sections correspond to Internal Nodes in the

hpvm/docs/how_to_guides/writing-heteroc-program.rst

 Writing a Hetero-C++ Program
-==========================
+============================
 
 The following document describes various programming patterns supported
 by the ``Hetero-C++`` api. Please refer to the `Hetero-C++ Language

hpvm/docs/tutorials/1-heterocpp.rst

@@ -8,7 +8,7 @@ a parallel dialect of C/C++ which describes hierarchical Task-level and Data-lev
 and compiles through HPVM.
 
 Writing a Program in Hetero-C++
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 We start with a scalar implementation of Matrix Multiplication written in ``C++``.
 
@@ -150,7 +150,7 @@ The `__hetero_launch` call generates the host code to prepare the arguments to b
 as well as generates HPVM Runtime method calls for managing memory between compute devices.
 
 Compiling the Program from Hetero-C++ to HPVM-C
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 To compile the above program, we first generate the LLVM IR Bitcode for the C++ file, using the following command: